webui: implement modular demo system with TypeScript and shared fixtures

Replace hand-written HTML demo pages with TypeScript demo modules and
automated infrastructure to reduce maintenance overhead and improve
developer experience with type safety and shared code.

Problems Solved:

Demo Maintenance Overhead:
- Hand-written HTML demo pages contained extensive boilerplate duplication
- No type checking for demo setup code or component data
- Manual maintenance of demo/index.html with available demos
- Difficult to share common fake data between demo pages
- No hot module replacement for demo development

Code Quality and Consistency:
- Demo setup code written in plain JavaScript without type safety
- No validation that demo data matches component interfaces
- Inconsistent styling and structure across demo pages
- Duplicated fake data declarations in each demo file

Solution Architecture:

TypeScript Demo Module System:
- Created DemoModule interface for standardized demo structure
- Demo modules export title, description, imports, and setup functions
- Full TypeScript compilation with type checking for demo code
- Dynamic import system for on-demand demo loading with Vite integration

Shared Demo Infrastructure:
- demo-framework/ with types.ts and demo-runner.ts for core functionality
- DemoRunner class handles dynamic loading, cleanup, and error handling
- Single demo-runner.html page loads any demo module dynamically
- Supports URL hash routing for direct demo links

Centralized Fake Data:
- demo-fixtures/ directory with shared TypeScript data files
- sampleToolCalls, sampleTimelineMessages, and sampleContainerState
- Type-safe imports ensure demo data matches component interfaces
- demoUtils with helper functions for consistent demo UI creation

Auto-generated Index Page:
- generate-index.ts scans for *.demo.ts files and extracts metadata
- Creates index-generated.html with links to all available demos
- Automatically includes demo titles and descriptions
- Eliminates manual maintenance of demo listing

Implementation Details:

Demo Framework:
- DemoRunner.loadDemo() uses dynamic imports with Vite ignore comments
- Automatic component import based on demo module configuration
- Support for demo-specific CSS and cleanup functions
- Error handling with detailed error display for debugging

Demo Module Structure:
- sketch-chat-input.demo.ts: Interactive chat with message history
- sketch-container-status.demo.ts: Status variations with real-time updates
- sketch-tool-calls.demo.ts: Multiple tool call examples with progressive loading
- All use shared fixtures and utilities for consistent experience

Vite Integration:
- Hot Module Replacement works for demo modules and shared fixtures
- TypeScript compilation on-the-fly for immediate feedback
- Dynamic imports work seamlessly with Vite's module system
- @vite-ignore comments prevent import analysis warnings

Testing and Validation:
- Tested demo runner loads and displays available components
- Verified component discovery and dynamic import functionality
- Confirmed shared fixture imports work correctly
- Validated auto-generated index creation and content

Files Modified:
- demo-framework/types.ts: TypeScript interfaces for demo system
- demo-framework/demo-runner.ts: Core demo loading and execution logic
- demo-fixtures/: Shared fake data (tool-calls.ts, timeline-messages.ts, container-status.ts, index.ts)
- demo-runner.html: Interactive demo browser with sidebar navigation
- generate-index.ts: Auto-generation script for demo index
- sketch-chat-input.demo.ts: Converted chat input demo to TypeScript
- sketch-container-status.demo.ts: Container status demo with variations
- sketch-tool-calls.demo.ts: Tool calls demo with interactive examples
- readme.md: Comprehensive documentation for new demo system

Benefits:
- Developers get full TypeScript type checking for demo code
- Shared fake data ensures consistency and reduces duplication
- Hot module replacement provides instant feedback during development
- Auto-generated index eliminates manual maintenance
- Modular architecture makes it easy to add new demos
- Vite integration provides fast development iteration

The new system reduces demo maintenance overhead while providing
better developer experience through TypeScript, shared code, and
automated infrastructure.

Co-Authored-By: sketch <hello@sketch.dev>
Change-ID: s3d91894eb7c4a79fk
diff --git a/webui/src/web-components/demo/demo-fixtures/container-status.ts b/webui/src/web-components/demo/demo-fixtures/container-status.ts
new file mode 100644
index 0000000..14c4964
--- /dev/null
+++ b/webui/src/web-components/demo/demo-fixtures/container-status.ts
@@ -0,0 +1,99 @@
+/**
+ * Shared fake container status data for demos
+ */
+
+import { State, CumulativeUsage } from "../../../types";
+
+export const sampleUsage: CumulativeUsage = {
+  start_time: "2024-01-15T10:00:00Z",
+  messages: 1337,
+  input_tokens: 25432,
+  output_tokens: 18765,
+  cache_read_input_tokens: 8234,
+  cache_creation_input_tokens: 12354,
+  total_cost_usd: 2.03,
+  tool_uses: {
+    bash: 45,
+    patch: 23,
+    think: 12,
+    "multiple-choice": 8,
+    keyword_search: 6,
+  },
+};
+
+export const sampleContainerState: State = {
+  state_version: 1,
+  message_count: 27,
+  total_usage: sampleUsage,
+  initial_commit: "decafbad42abc123",
+  slug: "file-upload-component",
+  branch_name: "sketch-wip",
+  branch_prefix: "sketch",
+  hostname: "example.hostname",
+  working_dir: "/app",
+  os: "linux",
+  git_origin: "https://github.com/user/repo.git",
+  outstanding_llm_calls: 0,
+  outstanding_tool_calls: null,
+  session_id: "session-abc123",
+  ssh_available: true,
+  in_container: true,
+  first_message_index: 0,
+  agent_state: "ready",
+  outside_hostname: "host.example.com",
+  inside_hostname: "container.local",
+  outside_os: "macOS",
+  inside_os: "linux",
+  outside_working_dir: "/Users/dev/project",
+  inside_working_dir: "/app",
+  todo_content:
+    "- Implement file upload component\n- Add drag and drop support\n- Write tests",
+  skaband_addr: "localhost:8080",
+  link_to_github: true,
+  ssh_connection_string: "ssh user@example.com",
+  diff_lines_added: 245,
+  diff_lines_removed: 67,
+};
+
+export const lightUsageState: State = {
+  ...sampleContainerState,
+  message_count: 5,
+  total_usage: {
+    ...sampleUsage,
+    messages: 5,
+    input_tokens: 1234,
+    output_tokens: 890,
+    total_cost_usd: 0.15,
+    tool_uses: {
+      bash: 2,
+      patch: 1,
+    },
+  },
+  diff_lines_added: 45,
+  diff_lines_removed: 12,
+};
+
+export const heavyUsageState: State = {
+  ...sampleContainerState,
+  message_count: 156,
+  total_usage: {
+    ...sampleUsage,
+    messages: 156,
+    input_tokens: 89234,
+    output_tokens: 67890,
+    cache_read_input_tokens: 23456,
+    cache_creation_input_tokens: 45678,
+    total_cost_usd: 12.45,
+    tool_uses: {
+      bash: 234,
+      patch: 89,
+      think: 67,
+      "multiple-choice": 23,
+      keyword_search: 45,
+      browser_navigate: 12,
+      codereview: 8,
+    },
+  },
+  diff_lines_added: 2847,
+  diff_lines_removed: 1456,
+};
diff --git a/webui/src/web-components/demo/demo-fixtures/index.ts b/webui/src/web-components/demo/demo-fixtures/index.ts
new file mode 100644
index 0000000..9a47f8e
--- /dev/null
+++ b/webui/src/web-components/demo/demo-fixtures/index.ts
@@ -0,0 +1,104 @@
+/**
+ * Centralized exports for all demo fixtures
+ */
+
+// Tool calls
+export {
+  sampleToolCalls,
+  longBashCommand,
+  multipleToolCallGroups,
+} from "./tool-calls";
+
+// Timeline messages
+export {
+  sampleTimelineMessages,
+  longTimelineMessage,
+  mixedTimelineMessages,
+} from "./timeline-messages";
+
+// Container status
+export {
+  sampleUsage,
+  sampleContainerState,
+  lightUsageState,
+  heavyUsageState,
+} from "./container-status";
+
+// Common demo utilities
+export const demoStyles = {
+  container: `
+    max-width: 1200px;
+    margin: 20px auto;
+    padding: 20px;
+    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+  `,
+
+  demoSection: `
+    margin: 20px 0;
+    padding: 15px;
+    border: 1px solid #e1e5e9;
+    border-radius: 8px;
+    background: #f8f9fa;
+  `,
+
+  demoHeader: `
+    font-size: 18px;
+    font-weight: 600;
+    margin-bottom: 10px;
+    color: #24292f;
+  `,
+};
+
+/**
+ * Common demo setup utilities
+ */
+export const demoUtils = {
+  /**
+   * Create a labeled demo section
+   */
+  createDemoSection(title: string, description?: string): HTMLElement {
+    const section = document.createElement("div");
+    section.style.cssText = demoStyles.demoSection;
+
+    const header = document.createElement("h3");
+    header.style.cssText = demoStyles.demoHeader;
+    header.textContent = title;
+    section.appendChild(header);
+
+    if (description) {
+      const desc = document.createElement("p");
+      desc.textContent = description;
+      desc.style.cssText = "color: #656d76; margin-bottom: 15px;";
+      section.appendChild(desc);
+    }
+
+    return section;
+  },
+
+  /**
+   * Wait for a specified number of milliseconds
+   */
+  delay(ms: number): Promise<void> {
+    return new Promise((resolve) => setTimeout(resolve, ms));
+  },
+
+  /**
+   * Create a simple button for demo interactions
+   */
+  createButton(text: string, onClick: () => void): HTMLButtonElement {
+    const button = document.createElement("button");
+    button.textContent = text;
+    button.style.cssText = `
+      padding: 8px 16px;
+      margin: 5px;
+      background: #0969da;
+      color: white;
+      border: none;
+      border-radius: 6px;
+      cursor: pointer;
+      font-size: 14px;
+    `;
+    button.addEventListener("click", onClick);
+    return button;
+  },
+};
diff --git a/webui/src/web-components/demo/demo-fixtures/timeline-messages.ts b/webui/src/web-components/demo/demo-fixtures/timeline-messages.ts
new file mode 100644
index 0000000..a98c728
--- /dev/null
+++ b/webui/src/web-components/demo/demo-fixtures/timeline-messages.ts
@@ -0,0 +1,113 @@
+/**
+ * Shared fake timeline message data for demos
+ */
+
+import { AgentMessage } from "../../../types";
+import { sampleToolCalls } from "./tool-calls";
+
+const baseTimestamp = new Date("2024-01-15T10:00:00Z");
+
+export const sampleTimelineMessages: AgentMessage[] = [
+  {
+    type: "user",
+    end_of_turn: true,
+    content:
+      "Can you help me implement a file upload component with drag and drop support?",
+    timestamp: new Date(baseTimestamp.getTime()).toISOString(),
+    conversation_id: "demo-conversation",
+    idx: 0,
+  },
+  {
+    type: "agent",
+    end_of_turn: false,
+    content:
+      "I'll help you create a file upload component with drag and drop support. Let me start by analyzing your current project structure and then implement the component.",
+    timestamp: new Date(baseTimestamp.getTime() + 1000).toISOString(),
+    conversation_id: "demo-conversation",
+    idx: 1,
+  },
+  {
+    type: "agent",
+    end_of_turn: false,
+    content: "First, let me check your current directory structure:",
+    tool_calls: [sampleToolCalls[2]], // bash command
+    timestamp: new Date(baseTimestamp.getTime() + 2000).toISOString(),
+    conversation_id: "demo-conversation",
+    idx: 2,
+  },
+  {
+    type: "tool",
+    end_of_turn: false,
+    content:
+      "src/\n├── components/\n│   ├── Button.tsx\n│   └── Input.tsx\n├── styles/\n│   └── globals.css\n└── utils/\n    └── helpers.ts",
+    tool_name: "bash",
+    tool_call_id: "toolu_01bash123",
+    timestamp: new Date(baseTimestamp.getTime() + 3000).toISOString(),
+    conversation_id: "demo-conversation",
+    idx: 3,
+  },
+  {
+    type: "agent",
+    end_of_turn: true,
+    content:
+      "Perfect! I can see you have a components directory. Now I'll create a FileUpload component with drag and drop functionality. This will include:\n\n1. A drop zone area\n2. File selection via click\n3. Progress indicators\n4. File validation\n5. Preview of selected files",
+    timestamp: new Date(baseTimestamp.getTime() + 4000).toISOString(),
+    conversation_id: "demo-conversation",
+    idx: 4,
+  },
+];
+
+export const longTimelineMessage: AgentMessage = {
+  type: "agent",
+  end_of_turn: true,
+  content: `I've analyzed your codebase and here's a comprehensive plan for implementing the file upload component:
+
+## Implementation Plan
+
+### 1. Component Structure
+The FileUpload component will be built using React with TypeScript. It will consist of:
+- A main container with drop zone styling
+- File input element (hidden)
+- Visual feedback for drag states
+- File list display area
+- Progress indicators
+
+### 2. Key Features
+- **Drag & Drop**: Full drag and drop support with visual feedback
+- **Multiple Files**: Support for selecting multiple files at once
+- **File Validation**: Size limits, file type restrictions
+- **Progress Tracking**: Upload progress for each file
+- **Error Handling**: User-friendly error messages
+- **Accessibility**: Proper ARIA labels and keyboard navigation
+
+### 3. Technical Considerations
+- Use the HTML5 File API for file handling
+- Implement proper event handlers for drag events
+- Add debouncing for performance
+- Include comprehensive error boundaries
+- Ensure mobile responsiveness
+
+### 4. Styling Approach
+- CSS modules for component-scoped styles
+- Responsive design with mobile-first approach
+- Smooth animations and transitions
+- Consistent with your existing design system
+
+This implementation will provide a robust, user-friendly file upload experience that integrates seamlessly with your existing application.`,
+  timestamp: new Date(baseTimestamp.getTime() + 5000).toISOString(),
+  conversation_id: "demo-conversation",
+  idx: 5,
+};
+
+export const mixedTimelineMessages: AgentMessage[] = [
+  ...sampleTimelineMessages,
+  longTimelineMessage,
+  {
+    type: "user",
+    end_of_turn: true,
+    content: "That sounds great! Can you also add file type validation?",
+    timestamp: new Date(baseTimestamp.getTime() + 6000).toISOString(),
+    conversation_id: "demo-conversation",
+    idx: 6,
+  },
+];
diff --git a/webui/src/web-components/demo/demo-fixtures/tool-calls.ts b/webui/src/web-components/demo/demo-fixtures/tool-calls.ts
new file mode 100644
index 0000000..eaa5009
--- /dev/null
+++ b/webui/src/web-components/demo/demo-fixtures/tool-calls.ts
@@ -0,0 +1,101 @@
+/**
+ * Shared fake tool call data for demos
+ */
+
+import { ToolCall } from "../../../types";
+
+export const sampleToolCalls: ToolCall[] = [
+  {
+    name: "multiple-choice",
+    input: JSON.stringify({
+      question: "What is your favorite programming language?",
+      choices: [
+        "JavaScript",
+        "TypeScript",
+        "Python",
+        "Go",
+        "Rust",
+        "Java",
+        "C#",
+        "C++",
+      ],
+    }),
+    tool_call_id: "toolu_01choice123",
+    result_message: {
+      type: "tool",
+      end_of_turn: false,
+      content: "Go",
+      tool_result: JSON.stringify({
+        selected: "Go",
+      }),
+      timestamp: new Date().toISOString(),
+      conversation_id: "demo-conversation",
+      idx: 1,
+    },
+  },
+  {
+    name: "multiple-choice",
+    input: JSON.stringify({
+      question: "Which feature would you like to implement next?",
+      choices: [
+        "Dark mode",
+        "User profiles",
+        "Social sharing",
+        "Analytics dashboard",
+      ],
+    }),
+    tool_call_id: "toolu_01choice456",
+    // No result yet, showing the choices without a selection
+  },
+  {
+    name: "bash",
+    input: JSON.stringify({
+      command:
+        "docker ps -a --format '{{.ID}} {{.Image }} {{.Names}}' | grep sketch | awk '{print $1 }' | xargs -I {} docker rm {} && docker image prune -af",
+    }),
+    tool_call_id: "toolu_01bash123",
+    result: "Removed containers and pruned images",
+  },
+  {
+    name: "patch",
+    input: JSON.stringify({
+      path: "/app/src/components/Button.tsx",
+      patches: [
+        {
+          operation: "replace",
+          oldText: "className='btn'",
+          newText: "className='btn btn-primary'",
+        },
+      ],
+    }),
+    tool_call_id: "toolu_01patch123",
+    result: "Applied patch successfully",
+  },
+  {
+    name: "think",
+    input: JSON.stringify({
+      thoughts:
+        "I need to analyze the user's requirements and break this down into smaller steps. The user wants to implement a file upload feature with drag-and-drop support.",
+    }),
+    tool_call_id: "toolu_01think123",
+    result: "Recorded thoughts for planning",
+  },
+];
+
+export const longBashCommand: ToolCall = {
+  name: "bash",
+  input: JSON.stringify({
+    command:
+      'git commit --allow-empty -m "chore: create empty commit with very long message\n\nThis is an extremely long commit message to demonstrate how Git handles verbose commit messages.\nThis empty commit has no actual code changes, but contains a lengthy explanation.\n\nThe empty commit pattern can be useful in several scenarios:\n1. Triggering CI/CD pipelines without modifying code\n2. Marking significant project milestones or releases\n3. Creating annotated reference points in the commit history\n4. Documenting important project decisions"',
+  }),
+  tool_call_id: "toolu_01longbash",
+  result:
+    "[main abc1234] chore: create empty commit with very long message\n\ncommit created successfully",
+};
+
+export const multipleToolCallGroups = [
+  [sampleToolCalls[0], sampleToolCalls[1]], // Multiple choice examples
+  [sampleToolCalls[2]], // Single bash command
+  [sampleToolCalls[3], sampleToolCalls[4]], // Patch and think
+  [longBashCommand], // Long command example
+];