fix(app): Web 平台兼容性修复 + 字体资源 + API base URL

- 添加 Web/Windows 平台支持 (flutter create --platforms)
- 下载字体资源 (NotoSansSC/Caveat Regular+Bold)
- Isar 3.x Web 不兼容：添加 kIsWeb 守卫，Web 上跳过 Isar 初始化
- IsarJournalRepository: instance 返回 nullable，Web 上使用 RemoteJournalRepository
- SyncEngine: persistPendingQueue/restorePendingQueue Web 安全
- SettingsBloc: 从 RepositoryProvider 改为 ListenableProvider
- ApiClient base URL: 8080 → 3000 匹配后端端口
- Isar .g.dart: 64 位 ID 替换为 JS 安全范围值

app/lib/app.dart

@@ -10,9 +10,11 @@
 // └─ BlocProvider<AuthBloc>
 //     └─ MaterialApp.router
 
+import 'package:flutter/foundation.dart' show kIsWeb;
 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 'core/theme/app_theme.dart';
 import 'core/routing/app_router.dart';
@@ -36,7 +38,10 @@ class NuanjiApp extends StatelessWidget {
     final apiClient = ApiClient();
     final authRepository = AuthRepository(apiClient: apiClient);
     // 离线优先：Isar 为主要本地仓库，Remote 供 SyncEngine 推送
-    final journalRepository = IsarJournalRepository();
+    // Web 平台：Isar 3.x 不支持 Web，直接使用远程仓库
+    final journalRepository = kIsWeb
+        ? RemoteJournalRepository(api: apiClient)
+        : IsarJournalRepository();
     final remoteJournalRepository = RemoteJournalRepository(api: apiClient);
     final syncEngine = SyncEngine(apiClient: apiClient);
     final classRepository = ClassRepository(api: apiClient);
@@ -67,18 +72,22 @@ class NuanjiApp extends StatelessWidget {
         RepositoryProvider<RemoteJournalRepository>.value(value: remoteJournalRepository),
         RepositoryProvider<SyncEngine>.value(value: syncEngine),
         RepositoryProvider<ClassRepository>.value(value: classRepository),
-        RepositoryProvider<SettingsBloc>.value(value: settingsBloc),
       ],
-      child: BlocProvider<AuthBloc>.value(
-        value: authBloc,
-        child: ListenableBuilder(
-        listenable: settingsBloc,
-        builder: (context, _) => _AppView(
-          router: createAppRouter(authBloc),
-          themeMode: settingsBloc.state.themeMode,
+      child: ListenableProvider<SettingsBloc>.value(
+        value: settingsBloc,
+        child: Builder(
+          builder: (context) {
+            final settings = context.watch<SettingsBloc>();
+            return BlocProvider<AuthBloc>.value(
+              value: authBloc,
+              child: _AppView(
+                router: createAppRouter(authBloc),
+                themeMode: settings.state.themeMode,
+              ),
+            );
+          },
         ),
       ),
-      ),
     );
   }
 }