fix(mining-app): fix Riverpod ref usage in router redirect callback

Use cached auth state from AuthNotifier instead of ref.read() to avoid
"Cannot use ref functions after provider changed" exception during rebuild.

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

frontend/mining-app/lib/core/router/app_router.dart

@@ -31,7 +31,8 @@ class AuthNotifier extends ChangeNotifier {
   void updateLoginState(bool isLoggedIn) {
     if (_isLoggedIn != isLoggedIn) {
       _isLoggedIn = isLoggedIn;
-      notifyListeners();
+      // 使用 Future.microtask 延迟通知，避免在 provider rebuild 期间触发
+      Future.microtask(() => notifyListeners());
     }
   }
 }
@@ -54,7 +55,8 @@ final appRouterProvider = Provider<GoRouter>((ref) {
     initialLocation: Routes.splash,
     refreshListenable: authNotifier,
     redirect: (context, state) {
-      final isLoggedIn = ref.read(isLoggedInProvider);
+      // 使用 authNotifier 中缓存的状态，而不是 ref.read
+      final isLoggedIn = authNotifier.isLoggedIn;
       final currentPath = state.uri.path;
 
       // splash 页面不做重定向，让它自己处理初始化逻辑