uf 액션 토스트 공통화 및 SnackBar 제거

userfront/lib/features/admin/presentation/user_management_screen.dart

@@ -3,6 +3,7 @@ import 'package:go_router/go_router.dart';
 import 'dart:async';
 import '../../../../core/services/auth_proxy_service.dart';
 import '../../../../core/i18n/locale_utils.dart';
+import '../../../../core/ui/toast_service.dart';
 
 class UserManagementScreen extends StatefulWidget {
   const UserManagementScreen({super.key});
@@ -108,12 +109,7 @@ class _UserManagementScreenState extends State<UserManagementScreen>
       }
     } else {
       if (mounted) {
-        ScaffoldMessenger.of(context).showSnackBar(
-          const SnackBar(
-            content: Text('Invalid Password'),
-            backgroundColor: Colors.red,
-          ),
-        );
+        ToastService.error('Invalid Password');
         context.go(buildLocalizedHomePath(Uri.base));
       }
     }
@@ -343,16 +339,12 @@ class _UserManagementScreenState extends State<UserManagementScreen>
   // --- UI Helpers ---
   void _showError(String msg) {
     if (!mounted) return;
-    ScaffoldMessenger.of(
-      context,
-    ).showSnackBar(SnackBar(content: Text(msg), backgroundColor: Colors.red));
+    ToastService.error(msg);
   }
 
   void _showSuccess(String msg) {
     if (!mounted) return;
-    ScaffoldMessenger.of(
-      context,
-    ).showSnackBar(SnackBar(content: Text(msg), backgroundColor: Colors.green));
+    ToastService.success(msg);
   }
 
   @override