feat(auth): 登录异常改为居中弹窗

lib/pages/auth/auth_view.dart

@@ -12,6 +12,7 @@ import '../../core/platform/keyboard_inset.dart';
 import '../../core/theme/app_colors.dart';
 import '../../core/theme/app_dimens.dart';
 import '../../core/theme/app_theme.dart';
+import '../../core/widgets/centered_error_dialog.dart';
 import '../../core/widgets/subpage_header.dart';
 import '../../l10n/app_localizations.dart';
 import 'auth_logic.dart';
@@ -227,6 +228,7 @@ class _AuthPageState extends State<AuthPage> {
       _logic.errorMessage = null;
     });
     final auth = context.read<AuthController>();
+    String? failureMessage;
     try {
       if (_logic.signUpMode) {
         await auth.register(
@@ -242,14 +244,18 @@ class _AuthPageState extends State<AuthPage> {
       if (!mounted) return;
       Navigator.of(context).maybePop();
     } on ApiException catch (error) {
-      if (!mounted) return;
-      setState(() => _logic.errorMessage = error.message);
+      failureMessage = error.message;
     } catch (_) {
-      if (!mounted) return;
-      setState(() => _logic.errorMessage = l10n.authNetworkError);
+      failureMessage = l10n.authNetworkError;
     } finally {
       if (mounted) setState(() => _logic.busy = false);
     }
+    if (!mounted || failureMessage == null) return;
+    await showCenteredErrorDialog(
+      context,
+      title: _logic.signUpMode ? l10n.authRegisterFailed : l10n.authLoginFailed,
+      message: failureMessage,
+    );
   }
 
   @override