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/sketch-chat-input.demo.ts b/webui/src/web-components/demo/sketch-chat-input.demo.ts
new file mode 100644
index 0000000..f18c0b9
--- /dev/null
+++ b/webui/src/web-components/demo/sketch-chat-input.demo.ts
@@ -0,0 +1,114 @@
+/**
+ * Demo module for sketch-chat-input component
+ */
+
+import { DemoModule } from "./demo-framework/types";
+import { demoUtils } from "./demo-fixtures/index";
+
+const demo: DemoModule = {
+  title: "Chat Input Demo",
+  description: "Interactive chat input component with send functionality",
+  imports: ["../sketch-chat-input"],
+
+  setup: async (container: HTMLElement) => {
+    // Create demo sections
+    const basicSection = demoUtils.createDemoSection(
+      "Basic Chat Input",
+      "Type a message and press Enter or click Send",
+    );
+
+    const messagesSection = demoUtils.createDemoSection(
+      "Chat Messages",
+      "Messages will appear here when sent",
+    );
+
+    // Create chat messages container
+    const messagesDiv = document.createElement("div");
+    messagesDiv.id = "chat-messages";
+    messagesDiv.style.cssText = `
+      min-height: 100px;
+      max-height: 200px;
+      overflow-y: auto;
+      border: 1px solid #d1d9e0;
+      border-radius: 6px;
+      padding: 10px;
+      margin-bottom: 10px;
+      background: #f6f8fa;
+    `;
+
+    // Create chat input
+    const chatInput = document.createElement("sketch-chat-input") as any;
+    chatInput.content = "Hello, how can I help you today?";
+
+    // Add message to display
+    const addMessage = (message: string, isUser: boolean = true) => {
+      const messageDiv = document.createElement("div");
+      messageDiv.style.cssText = `
+        padding: 8px 12px;
+        margin: 4px 0;
+        border-radius: 6px;
+        background: ${isUser ? "#0969da" : "#f1f3f4"};
+        color: ${isUser ? "white" : "#24292f"};
+        max-width: 80%;
+        margin-left: ${isUser ? "auto" : "0"};
+        margin-right: ${isUser ? "0" : "auto"};
+      `;
+      messageDiv.textContent = message;
+      messagesDiv.appendChild(messageDiv);
+      messagesDiv.scrollTop = messagesDiv.scrollHeight;
+    };
+
+    // Handle send events
+    chatInput.addEventListener("send-chat", (evt: any) => {
+      const message = evt.detail.message;
+      if (message.trim()) {
+        addMessage(message, true);
+        chatInput.content = "";
+
+        // Simulate bot response after a delay
+        setTimeout(() => {
+          const responses = [
+            "Thanks for your message!",
+            "I understand your request.",
+            "Let me help you with that.",
+            "That's a great question!",
+            "I'll look into that for you.",
+          ];
+          const randomResponse =
+            responses[Math.floor(Math.random() * responses.length)];
+          addMessage(randomResponse, false);
+        }, 1000);
+      }
+    });
+
+    // Add some sample messages
+    addMessage("Welcome to the chat demo!", false);
+    addMessage("This is a sample user message", true);
+
+    // Control buttons
+    const controlsDiv = document.createElement("div");
+    controlsDiv.style.cssText = "margin-top: 15px;";
+
+    const clearButton = demoUtils.createButton("Clear Messages", () => {
+      messagesDiv.innerHTML = "";
+      addMessage("Chat cleared!", false);
+    });
+
+    const presetButton = demoUtils.createButton("Add Preset Message", () => {
+      chatInput.content = "Can you help me implement a file upload component?";
+    });
+
+    controlsDiv.appendChild(clearButton);
+    controlsDiv.appendChild(presetButton);
+
+    // Assemble the demo
+    messagesSection.appendChild(messagesDiv);
+    basicSection.appendChild(chatInput);
+    basicSection.appendChild(controlsDiv);
+
+    container.appendChild(messagesSection);
+    container.appendChild(basicSection);
+  },
+};
+
+export default demo;