feat(mobile-app): 在主页添加随机3-6秒轮询检查维护状态

- 用户登录后在 HomeShellPage 每 3-6 秒（随机）检查一次维护状态
- 随机间隔可避免所有用户同时请求，减少服务器压力
- 后端发起维护后，用户最多 6 秒内会看到维护弹窗
- App 进入后台时暂停检查，恢复前台时立即检查并重启定时器
- 启动时、从后台恢复时也会立即检查一次

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/features/home/presentation/pages/home_shell_page.dart

@@ -7,6 +7,7 @@ import '../../../../core/theme/app_colors.dart';
 import '../../../../core/di/injection_container.dart';
 import '../../../../core/services/contract_check_service.dart';
 import '../../../../core/updater/update_service.dart';
+import '../../../../core/providers/maintenance_provider.dart';
 import '../../../../routes/route_paths.dart';
 import '../../../../routes/app_router.dart';
 import '../../../../bootstrap.dart';
@@ -33,6 +34,9 @@ class _HomeShellPageState extends ConsumerState<HomeShellPage>
   /// 后台合同检查定时器
   Timer? _contractCheckTimer;
 
+  /// 维护状态检查定时器
+  Timer? _maintenanceCheckTimer;
+
   /// 是否正在显示弹窗（防止重复弹窗）
   bool _isShowingDialog = false;
 
@@ -40,12 +44,15 @@ class _HomeShellPageState extends ConsumerState<HomeShellPage>
   void initState() {
     super.initState();
     WidgetsBinding.instance.addObserver(this);
-    // 首次进入时检查更新和未签署合同
+    // 首次进入时检查维护状态、更新和未签署合同
     WidgetsBinding.instance.addPostFrameCallback((_) {
+      _checkMaintenanceStatus();
       _checkForUpdateIfNeeded();
       _checkContractsAndKyc();
       // 启动后台定时检查
       _startBackgroundContractCheck();
+      // 启动维护状态定时检查
+      _startMaintenanceCheck();
     });
   }
 
@@ -53,19 +60,55 @@ class _HomeShellPageState extends ConsumerState<HomeShellPage>
   void dispose() {
     WidgetsBinding.instance.removeObserver(this);
     _contractCheckTimer?.cancel();
+    _maintenanceCheckTimer?.cancel();
     super.dispose();
   }
 
   @override
   void didChangeAppLifecycleState(AppLifecycleState state) {
-    // 从后台恢复时检查更新
+    // 从后台恢复时检查维护状态和更新
     if (state == AppLifecycleState.resumed) {
+      _checkMaintenanceStatus();
       _checkForUpdateIfNeeded();
       // 从后台恢复时也触发一次检查
       _scheduleNextContractCheck();
+      // 恢复维护检查定时器
+      _startMaintenanceCheck();
     } else if (state == AppLifecycleState.paused) {
       // 进入后台时取消定时器
       _contractCheckTimer?.cancel();
+      _maintenanceCheckTimer?.cancel();
+    }
+  }
+
+  /// 启动维护状态定时检查（随机 3-6 秒检查一次）
+  void _startMaintenanceCheck() {
+    _scheduleNextMaintenanceCheck();
+  }
+
+  /// 安排下一次维护检查
+  void _scheduleNextMaintenanceCheck() {
+    _maintenanceCheckTimer?.cancel();
+    // 随机 3-6 秒
+    final randomSeconds = 3 + Random().nextInt(4); // 3 + 0~3 = 3~6
+    _maintenanceCheckTimer = Timer(Duration(seconds: randomSeconds), () async {
+      await _checkMaintenanceStatus();
+      // 检查完成后安排下一次检查
+      if (mounted) {
+        _scheduleNextMaintenanceCheck();
+      }
+    });
+  }
+
+  /// 检查系统维护状态
+  Future<void> _checkMaintenanceStatus() async {
+    if (!mounted) return;
+
+    try {
+      final maintenanceNotifier = ref.read(maintenanceProvider.notifier);
+      await maintenanceNotifier.showMaintenanceDialogIfNeeded(context);
+    } catch (e) {
+      debugPrint('[HomeShellPage] 检查维护状态失败: $e');
     }
   }