feat: 添加 App 检查更新功能

- 前端：设置页面添加检查更新菜单项，从 pubspec.yaml 动态获取版本号
- 后端：新增 /api/v1/app/check-updates 接口，自动扫描 releases 目录对比版本
- 配置：新增 AppVersionSettings，支持通过环境变量配置版本和下载链接
- Docker：添加 releases 目录挂载

apps/lib/core/constants/app_constants.dart

@@ -0,0 +1,13 @@
+import 'package:package_info_plus/package_info_plus.dart';
+
+class AppConstants {
+  static String version = '0.1.0';
+  static int build = 1;
+
+  static Future<void> init() async {
+    final info = await PackageInfo.fromPlatform();
+    version = info.version;
+    final buildStr = info.buildNumber.isEmpty ? '1' : info.buildNumber;
+    build = int.tryParse(buildStr) ?? 1;
+  }
+}

apps/lib/core/di/injection.dart

@@ -15,6 +15,7 @@ import '../../features/calendar/data/services/calendar_service.dart';
 import '../../features/calendar/ui/calendar_state_manager.dart';
 import '../../features/friends/data/friends_api.dart';
 import '../../features/messages/data/inbox_api.dart';
+import '../../features/settings/data/settings_api.dart';
 import '../../features/users/data/users_api.dart';
 import '../../features/todo/data/todo_api.dart';
 
@@ -55,6 +56,9 @@ Future<void> configureDependencies() async {
   final friendsApi = FriendsApi(apiClient);
   sl.registerSingleton<FriendsApi>(friendsApi);
 
+  final settingsApi = SettingsApi(apiClient);
+  sl.registerSingleton<SettingsApi>(settingsApi);
+
   final inboxApi = InboxApi(apiClient);
   sl.registerSingleton<InboxApi>(inboxApi);