feat: 添加消息中心及顶栏未读角标功能

新增消息中心页面，实现未读消息轮询与展示
为各 Tab 页面顶栏添加通知图标及未读数角标
新增通知 API 接口与未读数状态管理
实现消息标记已读、全部已读及下拉刷新功能

lib/app/router.dart

@@ -7,6 +7,7 @@ import '../features/auth/application/session_controller.dart';
 import '../features/auth/presentation/login_page.dart';
 import '../features/customer/presentation/customer_detail_page.dart';
 import '../features/customer/presentation/customer_edit_page.dart';
+import '../features/notice/presentation/notice_center_page.dart';
 import '../features/project/presentation/project_detail_page.dart';
 import '../features/survey/presentation/survey_form_page.dart';
 import '../features/survey/presentation/survey_list_page.dart';
@@ -50,6 +51,12 @@ final routerProvider = Provider<GoRouter>((ref) {
       GoRoute(path: '/login', builder: (context, state) => const LoginPage()),
       GoRoute(path: '/tabs', builder: (context, state) => const TabsPage()),
 
+      // 消息中心（二级页）
+      GoRoute(
+        path: '/notice',
+        builder: (context, state) => const NoticeCenterPage(),
+      ),
+
       // 客户模块
       GoRoute(
         path: '/customer/detail/:id',