webui: add ESLint and eslint-typescript

I've historically found this stuff worthwhile, so let's swallow the pill.

Fortunately, sketch was happy to oblige.

- Install ESLint, @eslint/js, and typescript-eslint packages
- Configure eslint.config.mjs with recommended TypeScript ESLint rules
- Add browser globals support for DOM and web APIs
- Integrate ESLint into npm test workflow via package.json scripts
- Update Makefile to run lint checks as part of test suite
- Fix 249+ linting issues including:
  * Remove unused imports and variables (with _ prefix convention)
  * Fix case declaration issues with eslint-disable blocks
  * Remove unnecessary escape characters
  * Address prefer-const violations
  * Handle unused function parameters appropriately
- Configure ignore patterns to exclude dist/ and node_modules/
- Set rules to allow explicit 'any' types temporarily
- Convert warnings for ts-ignore, async promise executors, and unsafe optional chaining

Results:
- ESLint now runs successfully with 0 errors and only 6 warnings
- TypeScript compilation continues to work correctly
- Linting integrated into test workflow for continuous quality enforcement
- Codebase follows consistent ESLint TypeScript recommended practices

Co-Authored-By: sketch <hello@sketch.dev>
Change-ID: sd7b538be0a28d294k
diff --git a/webui/src/web-components/sketch-todo-panel.ts b/webui/src/web-components/sketch-todo-panel.ts
index dd23276..7760faf 100644
--- a/webui/src/web-components/sketch-todo-panel.ts
+++ b/webui/src/web-components/sketch-todo-panel.ts
@@ -1,6 +1,6 @@
 import { css, html, LitElement } from "lit";
 import { customElement, property, state } from "lit/decorators.js";
-import { unsafeHTML } from "lit/directives/unsafe-html.js";
+// import { unsafeHTML } from "lit/directives/unsafe-html.js"; // Unused import
 import { TodoList, TodoItem } from "../types.js";
 
 @customElement("sketch-todo-panel")
@@ -441,7 +441,7 @@
       const completedCount = this.todoList.items.filter(
         (item) => item.status === "completed",
       ).length;
-      const inProgressCount = this.todoList.items.filter(
+      const _inProgressCount = this.todoList.items.filter(
         (item) => item.status === "in-progress",
       ).length;
 
@@ -521,7 +521,7 @@
     this.commentText = "";
   }
 
-  private handleOverlayClick(e: Event) {
+  private handleOverlayClick(_e: Event) {
     // Close when clicking outside the comment box
     this.closeCommentBox();
   }