feat: migrate from React to Preact, add Vitest testing, and optimize bundle

Major framework and tooling changes:
- Migrate from React 19 to Preact 10 with preact-iso for routing
- Replace @mantine/hooks with custom hooks (useBooleanToggle, useViewportSize)
- Switch from @heroicons/react to lucide-preact for icons
- Replace chance.js with random-js for RNG

Testing infrastructure:
- Add Vitest with @testing-library/preact and happy-dom
- Set up test configuration and initial App tests
- Add Vitest UI for interactive test running

Build optimizations:
- Add cssnano for CSS minification
- Configure aggressive bundle optimizations in Vite
- Update to Tailwind CSS 4.1.17

Project structure:
- Consolidate entry point from main.tsx to index.tsx
- Reorganize CSS location (styles/index.css → index.css)
- Add ESLint with preact config
- Update TypeScript configuration for Preact

tsconfig.json

@@ -1,25 +1,25 @@
 {
   "compilerOptions": {
-    "target": "ESNext",
-    "useDefineForClassFields": true,
-    "lib": ["DOM", "DOM.Iterable", "ESNext"],
-    "allowJs": false,
-    "skipLibCheck": true,
-    "esModuleInterop": false,
-    "allowSyntheticDefaultImports": true,
-    "strict": true,
-    "forceConsistentCasingInFileNames": true,
+    "target": "ES2020",
     "module": "ESNext",
-    "moduleResolution": "Node",
-    "resolveJsonModule": true,
-    "isolatedModules": true,
+    "moduleResolution": "bundler",
+    "lib": ["DOM", "DOM.Iterable", "ESNext"],
     "noEmit": true,
+    "allowJs": true,
+    "checkJs": true,
+
+    /* Preact Config */
     "jsx": "react-jsx",
-    "baseUrl": "./src/",
+    "jsxImportSource": "preact",
+    "skipLibCheck": true,
+    "baseUrl": "./",
     "paths": {
-      "@/*": ["./*"]
-    }
+      "react": ["node_modules/preact/compat/"],
+      "react-dom": ["node_modules/preact/compat/"],
+      "@/*": ["src/*"]
+    },
+
+    "outDir": "./dist"
   },
-  "include": ["src"],
-  "references": [{ "path": "./tsconfig.node.json" }]
+  "include": ["node_modules/vite/client.d.ts", "src"]
 }