feat: enforce hierarchical back navigation and home-only exit

apps/lib/features/settings/ui/screens/settings_screen.dart

@@ -20,6 +20,7 @@ import 'package:social_app/features/settings/data/settings_api.dart';
 import 'package:social_app/features/settings/data/services/settings_user_cache.dart';
 import 'package:social_app/features/users/data/models/user_response.dart';
 import 'package:social_app/features/users/data/users_api.dart';
+import 'package:social_app/features/home/ui/navigation/home_return_policy.dart';
 import '../widgets/settings_page_scaffold.dart';
 
 const settingsProfileEditButtonKey = ValueKey('settings_profile_edit_button');
@@ -90,7 +91,7 @@ class _SettingsScreenState extends State<SettingsScreen> {
   Widget build(BuildContext context) {
     return SettingsPageScaffold(
       title: '设置',
-      onBack: () => context.pop(),
+      onBack: () => returnToHomePreserveState(context, forceGoHome: true),
       body: Column(
         crossAxisAlignment: CrossAxisAlignment.stretch,
         children: [