Initial project

apps/im_app/lib/app/app.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../core/ui/base/app_theme.dart';
+import 'di/app_providers.dart';
+import 'di/network_provider.dart';
+import 'router/app_router.dart';
+
+/// 应用根组件
+///
+/// 职责：
+/// - 路由配置（go_router，含登录守卫）
+/// - 主题配置（亮色 / 暗色 / 跟随系统）
+/// - App 生命周期监听（前后台切换 → WebSocket 断连/重连）
+/// - 启动初始化（[AppInitializer] 两阶段串行队列）
+///
+/// ## 启动初始化
+///
+/// 通过 [appInitializerProvider] 声明任务，两阶段串行执行：
+/// - Critical：首帧前，只放必须阻塞的任务
+/// - Deferred：首帧后，不争抢资源、不卡 UI
+///
+/// 详见 [AppInitializer] 文档。
+class IMApp extends ConsumerStatefulWidget {
+  const IMApp({super.key});
+
+  @override
+  ConsumerState<IMApp> createState() => _IMAppState();
+}
+
+class _IMAppState extends ConsumerState<IMApp> with WidgetsBindingObserver {
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addObserver(this);
+    ref.read(appInitializerProvider).run();
+  }
+
+  @override
+  void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
+    super.dispose();
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    final socketManager = ref.read(socketManagerProvider);
+
+    switch (state) {
+      case AppLifecycleState.resumed:
+        socketManager.onEnterForeground();
+      case AppLifecycleState.paused:
+        socketManager.onEnterBackground();
+      case AppLifecycleState.inactive:
+      case AppLifecycleState.detached:
+      case AppLifecycleState.hidden:
+        break;
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp.router(
+      title: 'IM App', // TODO: 接入国际化
+      theme: AppTheme.theme,
+      darkTheme: AppTheme.darkTheme,
+      themeMode: ref.watch(themeModeProvider),
+      routerConfig: ref.watch(routerProvider),
+    );
+  }
+}