fix(mobile-app): 简化退出登录提示文案

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

frontend/mobile-app/lib/features/profile/presentation/pages/profile_page.dart

@@ -4228,7 +4228,7 @@ class _ProfilePageState extends ConsumerState<ProfilePage> {
       context: context,
       builder: (context) => AlertDialog(
         title: const Text('退出登录'),
-        content: const Text('确定要退出当前账号吗？\n\n退出后账号数据会保留在本地，可在账号切换页面重新登录。'),
+        content: const Text('确定要退出当前账号吗？'),
         actions: [
           TextButton(
             onPressed: () => Navigator.of(context).pop(),