feat(ui): migrate Flutter UI library to Next.js 16 (App Router)

Migrate all 87 Dart files from /Users/chase/Documents/cozsweet/lib/ui/
to TypeScript React components, replacing Flutter-native features with
Web equivalents and reimplementing the BLoC pattern with React
Context + useReducer.

Highlights
- 1:1 BLoC -> Context+useReducer+side-effects mapping for auth, chat,
  user, and sidebar features (4 providers wired in root-providers.tsx)
- 500px MobileShell primitive eliminates per-screen layout boilerplate
- Headless Dialog primitive (createPortal + ESC + scroll lock) powers
  quota / pwa-install / username / pronouns / subscription / other-options
  dialogs
- New integrations/: facebook-sdk, google-identity, pwa-install,
  media-recorder (Web Speech API + MediaRecorder), browser-detect,
  chat-websocket (singleton), message-queue (throttled send)
- CSS Modules + existing design tokens (no new styling system);
  extended with breakpoints.css and dimensions.css
- Custom hooks: useBreakpoint (useSyncExternalStore),
  useFullVisibility (IntersectionObserver), usePwaInstall,
  usePullToRefresh
- Vitest + jsdom; 15 unit tests (chat-reducer, auth-validators)
- React 19.2.4, Next.js 16.2.7, Zod 4, lottie-react, classnames

Workarounds
- next.config.ts: experimental.staticGenerationRetryCount = 0 to
  bypass Next.js 16.2.7 /_global-error workStore prerender bug
- src/app/global-error.tsx: required Client Component
- src/types/globals.d.ts: centralized window.google / FB /
  SpeechRecognition declarations

Routes (/, /splash, /auth, /chat, /chat/deviceid/[deviceId],
/sidebar) all build and lint clean.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -8,13 +8,18 @@
     "start": "next start",
     "lint": "eslint",
     "lint:fix": "eslint --fix",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "test:ui": "vitest --ui",
     "generate-barrels": "barrelsby --delete -c barrelsby.json"
   },
   "dependencies": {
     "@fingerprintjs/fingerprintjs": "^5.2.0",
     "@greatsumini/react-facebook-login": "^3.4.0",
     "@react-oauth/google": "^0.13.5",
+    "classnames": "^2.5.1",
     "dexie": "^4.4.3",
+    "lottie-react": "^2.4.1",
     "next": "16.2.7",
     "ofetch": "^1.5.1",
     "react": "19.2.4",
@@ -26,10 +31,14 @@
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
+    "@vitest/coverage-v8": "^4.1.8",
+    "@vitest/ui": "^4.1.8",
     "barrelsby": "^2.8.1",
     "eslint": "^9",
     "eslint-config-next": "16.2.7",
+    "jsdom": "^29.1.1",
     "tailwindcss": "^4",
-    "typescript": "^5"
+    "typescript": "^5",
+    "vitest": "^4.1.8"
   }
 }