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/features/customer/presentation/customer_tab.dart

@@ -5,6 +5,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
 import '../../../app/tab_index.dart';
+import '../../../core/providers.dart';
 import '../../../core/theme/app_colors.dart';
 import '../../../core/theme/app_dimens.dart';
 import '../../../core/theme/app_typography.dart';
@@ -134,6 +135,8 @@ class _CustomerTabState extends ConsumerState<CustomerTab> {
           topBar: XTopBar.brand(
             title: '鑫潼智电',
             trailingColor: AppColors.primary,
+            onTrailingTap: () => context.push('/notice'),
+            trailingBadge: ref.watch(noticeUnreadCountProvider),
           ),
           child: Column(
             crossAxisAlignment: CrossAxisAlignment.stretch,