feat(app): D.3 中等优先级 UX 改进 — 保存指示器 + 触摸目标 + 主题持久化

D.3.2 三态保存指示器:
- 未保存 (灰色) → 保存中 (琥珀色脉冲点) → 已保存 (绿色点)
- _PulsingDot 动画组件，800ms 呼吸效果
- 点击'完成'时显示保存中状态

D.3.3 工具栏触摸目标:
- BoxConstraints 36x36 → 44x44，符合 WCAG 标准

D.3.4 主题偏好持久化:
- SettingsBloc 接受 SharedPreferences，保存/恢复 themeMode
- NuanjiApp 改为 StatefulWidget，异步初始化 SharedPreferences
- 启动时显示 loading，初始化完成后渲染 app

app/lib/app.dart

@@ -15,6 +15,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:go_router/go_router.dart';
 import 'package:provider/provider.dart' show ListenableProvider;
+import 'package:shared_preferences/shared_preferences.dart';
 
 import 'config/app_config.dart';
 import 'core/theme/app_theme.dart';
@@ -31,70 +32,99 @@ import 'features/auth/bloc/auth_bloc.dart';
 import 'features/profile/bloc/settings_bloc.dart';
 
 /// 暖记 App — 根组件
-class NuanjiApp extends StatelessWidget {
+class NuanjiApp extends StatefulWidget {
   const NuanjiApp({super.key});
 
   @override
-  Widget build(BuildContext context) {
-    // 创建全局依赖（App 生命周期内单例）
-    // 开发模式默认使用 localhost，可通过 --dart-define 覆盖
+  State<NuanjiApp> createState() => _NuanjiAppState();
+}
+
+class _NuanjiAppState extends State<NuanjiApp> {
+  late final ApiClient _apiClient;
+  late final AuthRepository _authRepository;
+  late final JournalRepository _journalRepository;
+  late final RemoteJournalRepository _remoteJournalRepository;
+  late final SyncEngine _syncEngine;
+  late final ClassRepository _classRepository;
+  late final SettingsBloc _settingsBloc;
+  late final AuthBloc _authBloc;
+
+  bool _initialized = false;
+
+  @override
+  void initState() {
+    super.initState();
+    _initApp();
+  }
+
+  Future<void> _initApp() async {
     final config = kDebugMode ? AppConfig.dev : AppConfig.fromEnvironment();
-    final apiClient = ApiClient(baseUrl: config.apiBaseUrl);
+    _apiClient = ApiClient(baseUrl: config.apiBaseUrl);
     final tokenStore = createSecureTokenStore();
-    final authRepository = AuthRepository(apiClient: apiClient, tokenStore: tokenStore);
-    // 离线优先：Isar 为主要本地仓库，Remote 供 SyncEngine 推送
-    // Web 平台：Isar 3.x 不支持 Web，直接使用远程仓库
-    final journalRepository = kIsWeb
-        ? RemoteJournalRepository(api: apiClient)
+    _authRepository = AuthRepository(apiClient: _apiClient, tokenStore: tokenStore);
+    _journalRepository = kIsWeb
+        ? RemoteJournalRepository(api: _apiClient)
         : IsarJournalRepository();
-    final remoteJournalRepository = RemoteJournalRepository(api: apiClient);
-    final syncEngine = SyncEngine(apiClient: apiClient);
-    final classRepository = ClassRepository(api: apiClient);
-    final settingsBloc = SettingsBloc();
-    final authBloc = AuthBloc(
-      authRepository: authRepository,
-      classRepository: classRepository,
+    _remoteJournalRepository = RemoteJournalRepository(api: _apiClient);
+    _syncEngine = SyncEngine(apiClient: _apiClient);
+    _classRepository = ClassRepository(api: _apiClient);
+    _settingsBloc = SettingsBloc(
+      prefs: await SharedPreferences.getInstance(),
+    );
+    _authBloc = AuthBloc(
+      authRepository: _authRepository,
+      classRepository: _classRepository,
     );
 
     // 启动时检查认证状态
-    authBloc.add(const AppStarted());
+    _authBloc.add(const AppStarted());
 
-    // 异步恢复 SyncEngine 持久化队列（fire-and-forget，不阻塞 UI）
-    syncEngine.restorePendingQueue();
-    // 启动网络监听 — 网络恢复时自动触发 trySync()
-    syncEngine.startAutoSync();
+    // 异步恢复 SyncEngine 持久化队列
+    _syncEngine.restorePendingQueue();
+    _syncEngine.startAutoSync();
 
     // 认证状态监听：登出时清除 token
-    // 注意：登录时 token 由 AuthRepository.login() 直接注入 ApiClient
-    authBloc.stream.listen((state) {
+    _authBloc.stream.listen((state) {
       if (state is! Authenticated) {
-        apiClient.clearToken();
+        _apiClient.clearToken();
       }
     });
 
-    // Token 刷新彻底失败时 → 派发 AuthExpired → 路由重定向到登录页
-    apiClient.onAuthFailed = () {
-      authBloc.add(const AuthExpired());
+    // Token 刷新彻底失败时 → 派发 AuthExpired
+    _apiClient.onAuthFailed = () {
+      _authBloc.add(const AuthExpired());
     };
 
+    setState(() => _initialized = true);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    if (!_initialized) {
+      return const MaterialApp(
+        debugShowCheckedModeBanner: false,
+        home: Scaffold(body: Center(child: CircularProgressIndicator())),
+      );
+    }
+
     return MultiRepositoryProvider(
       providers: [
-        RepositoryProvider<ApiClient>.value(value: apiClient),
-        RepositoryProvider<AuthRepository>.value(value: authRepository),
-        RepositoryProvider<JournalRepository>.value(value: journalRepository),
-        RepositoryProvider<RemoteJournalRepository>.value(value: remoteJournalRepository),
-        RepositoryProvider<SyncEngine>.value(value: syncEngine),
-        RepositoryProvider<ClassRepository>.value(value: classRepository),
+        RepositoryProvider<ApiClient>.value(value: _apiClient),
+        RepositoryProvider<AuthRepository>.value(value: _authRepository),
+        RepositoryProvider<JournalRepository>.value(value: _journalRepository),
+        RepositoryProvider<RemoteJournalRepository>.value(value: _remoteJournalRepository),
+        RepositoryProvider<SyncEngine>.value(value: _syncEngine),
+        RepositoryProvider<ClassRepository>.value(value: _classRepository),
       ],
       child: ListenableProvider<SettingsBloc>.value(
-        value: settingsBloc,
+        value: _settingsBloc,
         child: Builder(
           builder: (context) {
             final settings = context.watch<SettingsBloc>();
             return BlocProvider<AuthBloc>.value(
-              value: authBloc,
+              value: _authBloc,
               child: _AppView(
-                router: createAppRouter(authBloc),
+                router: createAppRouter(_authBloc),
                 themeMode: settings.state.themeMode,
               ),
             );