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/integrations/message-queue.ts

@@ -0,0 +1,74 @@
+/**
+ * 消息发送队列（限流）
+ *
+ * 原始 Dart: lib/core/net/message_queue.dart
+ *
+ * 业务行为：
+ *   - 入队消息按 `intervalMs` 间隔逐条发送（默认 1000ms）
+ *   - 消费者可声明每条消息是否成功消费；不成功则重新入队
+ *   - 队列可在任意时刻清空（dispose）
+ */
+export type MessageConsumer = (content: string) => boolean | Promise<boolean>;
+
+export class MessageQueue {
+  private queue: string[] = [];
+  private timer: ReturnType<typeof setTimeout> | null = null;
+  private disposed = false;
+  private consumer: MessageConsumer | null = null;
+
+  constructor(private readonly intervalMs = 1000) {}
+
+  /** 注册消费者（消费者必须能处理失败/重试）。 */
+  setConsumer(consumer: MessageConsumer): void {
+    this.consumer = consumer;
+  }
+
+  enqueue(content: string): void {
+    if (this.disposed) return;
+    this.queue.push(content);
+    if (!this.timer) this.scheduleNext();
+  }
+
+  private async attemptSend(next: string): Promise<void> {
+    if (!this.consumer) {
+      this.queue.unshift(next);
+      return;
+    }
+    let ok = false;
+    try {
+      ok = await this.consumer(next);
+    } catch (e) {
+      console.error("[MessageQueue] consumer error", e);
+      ok = false;
+    }
+    if (!ok) {
+      // 消费失败，放回队首等待下次
+      this.queue.unshift(next);
+    }
+  }
+
+  private scheduleNext(): void {
+    if (this.disposed) return;
+    const next = this.queue.shift();
+    if (next === undefined) {
+      this.timer = null;
+      return;
+    }
+    this.timer = setTimeout(() => {
+      void this.attemptSend(next).finally(() => this.scheduleNext());
+    }, this.intervalMs);
+  }
+
+  clear(): void {
+    this.queue = [];
+  }
+
+  dispose(): void {
+    this.disposed = true;
+    this.clear();
+    if (this.timer) {
+      clearTimeout(this.timer);
+      this.timer = null;
+    }
+  }
+}