feat(auth): 登录异常改为居中弹窗

lib/core/widgets/centered_error_dialog.dart

@@ -0,0 +1,67 @@
+// Author: fruit.com.cn
+
+import 'package:flutter/material.dart';
+
+import '../../l10n/app_localizations.dart';
+import '../theme/app_colors.dart';
+
+const Key _dialogKey = Key('centered-error-dialog');
+const Key _confirmKey = Key('centered-error-confirm');
+const double _dialogRadius = 16;
+const double _titleHorizontalInset = 24;
+const double _titleTopInset = 24;
+const double _contentHorizontalInset = 24;
+const double _contentTopInset = 12;
+const double _contentBottomInset = 8;
+const double _actionsHorizontalInset = 16;
+const double _actionsBottomInset = 12;
+const EdgeInsets _titlePadding = EdgeInsets.fromLTRB(
+  _titleHorizontalInset,
+  _titleTopInset,
+  _titleHorizontalInset,
+  0,
+);
+const EdgeInsets _contentPadding = EdgeInsets.fromLTRB(
+  _contentHorizontalInset,
+  _contentTopInset,
+  _contentHorizontalInset,
+  _contentBottomInset,
+);
+const EdgeInsets _actionsPadding = EdgeInsets.fromLTRB(
+  _actionsHorizontalInset,
+  0,
+  _actionsHorizontalInset,
+  _actionsBottomInset,
+);
+
+/// Shows a reusable error dialog centered on the screen.
+Future<void> showCenteredErrorDialog(
+  BuildContext context, {
+  required String title,
+  required String message,
+}) async {
+  final l10n = AppLocalizations.of(context)!;
+  await showDialog<void>(
+    context: context,
+    barrierDismissible: true,
+    builder: (dialogContext) => AlertDialog(
+      key: _dialogKey,
+      backgroundColor: AppColors.card,
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(_dialogRadius),
+      ),
+      titlePadding: _titlePadding,
+      contentPadding: _contentPadding,
+      title: Text(title),
+      content: Text(message),
+      actionsPadding: _actionsPadding,
+      actions: [
+        TextButton(
+          key: _confirmKey,
+          onPressed: () => Navigator.of(dialogContext).pop(),
+          child: Text(l10n.authErrorConfirm),
+        ),
+      ],
+    ),
+  );
+}