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>

src/types/globals.d.ts

@@ -0,0 +1,115 @@
+/**
+ * 全局 Window 增强
+ *
+ * 集中声明第三方 SDK 在 window 上挂载的全局变量。
+ * 单文件能让 TS 编译器在全局范围找到这些属性。
+ */
+export {};
+
+declare global {
+  interface Window {
+    google?: {
+      accounts: {
+        id: {
+          initialize(params: {
+            client_id: string;
+            callback: (response: { credential?: string; select_by?: string }) => void;
+            auto_select?: boolean;
+            cancel_on_tap_outside?: boolean;
+          }): void;
+          prompt(): void;
+          renderButton(
+            parent: HTMLElement,
+            options: {
+              type?: "standard" | "icon";
+              theme?: "outline" | "filled_blue" | "filled_black";
+              size?: "large" | "medium" | "small";
+              text?: "signin_with" | "signup_with" | "continue_with" | "signin";
+              shape?: "rectangular" | "pill" | "circle" | "square";
+              logo_alignment?: "left" | "center";
+              width?: number;
+              locale?: string;
+            },
+          ): void;
+          disableAutoSelect(): void;
+        };
+      };
+    };
+    FB?: {
+      init(params: {
+        appId: string;
+        cookie?: boolean;
+        xfbml?: boolean;
+        version: string;
+      }): void;
+      login(
+        callback: (response: {
+          authResponse?: {
+            accessToken: string;
+            userID: string;
+            expiresIn: number;
+          };
+          status?: "connected" | "not_authorized" | "unknown";
+        }) => void,
+        options?: { scope: string },
+      ): void;
+      logout(callback?: () => void): void;
+      api(
+        path: string,
+        callback: (response: {
+          id?: string;
+          name?: string;
+          email?: string;
+          picture?: { data?: { url?: string } };
+        }) => void,
+      ): void;
+    };
+    fbAsyncInit?: () => void;
+
+    // Web Speech API
+    SpeechRecognition?: new () => SpeechRecognitionInstance;
+    webkitSpeechRecognition?: new () => SpeechRecognitionInstance;
+  }
+
+  interface SpeechRecognitionInstance extends EventTarget {
+    lang: string;
+    continuous: boolean;
+    interimResults: boolean;
+    maxAlternatives: number;
+    onresult: ((event: SpeechRecognitionEvent) => void) | null;
+    onerror: ((event: SpeechRecognitionErrorEvent) => void) | null;
+    onend: ((event: Event) => void) | null;
+    onstart: ((event: Event) => void) | null;
+    start(): void;
+    stop(): void;
+    abort(): void;
+  }
+
+  interface SpeechRecognitionEvent extends Event {
+    resultIndex: number;
+    results: SpeechRecognitionResultList;
+  }
+
+  interface SpeechRecognitionErrorEvent extends Event {
+    error: string;
+    message: string;
+  }
+
+  interface SpeechRecognitionResultList {
+    readonly length: number;
+    item(index: number): SpeechRecognitionResult;
+    [index: number]: SpeechRecognitionResult;
+  }
+
+  interface SpeechRecognitionResult {
+    readonly length: number;
+    item(index: number): SpeechRecognitionAlternative;
+    isFinal: boolean;
+    [index: number]: SpeechRecognitionAlternative;
+  }
+
+  interface SpeechRecognitionAlternative {
+    transcript: string;
+    confidence: number;
+  }
+}