fix(sms-scan): 에러 메시지를 토스트로 변경

- 구독 정보를 찾지 못한 경우 상단 붉은색 텍스트 대신 하단 토스트 메시지 출력
- ScanInitialWidget에서 errorMessage 파라미터 제거
- SmsScanController에서 AppSnackBar.showError() 사용
- 불필요한 _errorMessage 상태 변수 제거

lib/controllers/sms_scan_controller.dart

@@ -17,15 +17,13 @@ import '../providers/category_provider.dart';
 import '../providers/payment_card_provider.dart';
 import '../l10n/app_localizations.dart';
 import '../utils/logger.dart';
+import '../widgets/common/snackbar/app_snackbar.dart';
 
 class SmsScanController extends ChangeNotifier {
   // 상태 관리
   bool _isLoading = false;
   bool get isLoading => _isLoading;
 
-  String? _errorMessage;
-  String? get errorMessage => _errorMessage;
-
   List<Subscription> _scannedSubscriptions = [];
   List<Subscription> get scannedSubscriptions => _scannedSubscriptions;
   PaymentCardSuggestion? _currentSuggestion;
@@ -109,7 +107,6 @@ class SmsScanController extends ChangeNotifier {
 
   Future<void> scanSms(BuildContext context) async {
     _isLoading = true;
-    _errorMessage = null;
     _scannedSubscriptions = [];
     _currentIndex = 0;
     notifyListeners();
@@ -137,9 +134,12 @@ class SmsScanController extends ChangeNotifier {
           final req = await permission.Permission.sms.request();
           if (!ctx.mounted) return;
           if (!req.isGranted) {
-            // 거부됨: 안내 후 종료
+            // 거부됨: 토스트 표시 후 종료
             if (!ctx.mounted) return;
-            _errorMessage = AppLocalizations.of(ctx).smsPermissionRequired;
+            AppSnackBar.showError(
+              context: ctx,
+              message: AppLocalizations.of(ctx).smsPermissionRequired,
+            );
             _isLoading = false;
             notifyListeners();
             return;
@@ -162,7 +162,10 @@ class SmsScanController extends ChangeNotifier {
 
       if (scanResults.isEmpty) {
         Log.i('스캔된 구독이 없음');
-        _errorMessage = AppLocalizations.of(context).subscriptionNotFound;
+        AppSnackBar.showError(
+          context: context,
+          message: AppLocalizations.of(context).subscriptionNotFound,
+        );
         _isLoading = false;
         notifyListeners();
         return;
@@ -184,7 +187,10 @@ class SmsScanController extends ChangeNotifier {
 
       if (repeatSubscriptions.isEmpty) {
         Log.i('반복 결제된 구독이 없음');
-        _errorMessage = AppLocalizations.of(context).repeatSubscriptionNotFound;
+        AppSnackBar.showError(
+          context: context,
+          message: AppLocalizations.of(context).repeatSubscriptionNotFound,
+        );
         _isLoading = false;
         notifyListeners();
         return;
@@ -223,8 +229,10 @@ class SmsScanController extends ChangeNotifier {
     } catch (e) {
       Log.e('SMS 스캔 중 오류 발생', e);
       if (context.mounted) {
-        _errorMessage =
-            AppLocalizations.of(context).smsScanErrorWithMessage(e.toString());
+        AppSnackBar.showError(
+          context: context,
+          message: AppLocalizations.of(context).smsScanErrorWithMessage(e.toString()),
+        );
         _isLoading = false;
         notifyListeners();
       }
@@ -343,7 +351,6 @@ class SmsScanController extends ChangeNotifier {
   void resetState() {
     _scannedSubscriptions = [];
     _currentIndex = 0;
-    _errorMessage = null;
     _selectedPaymentCardId = null;
     _currentSuggestion = null;
     _shouldSuggestCardCreation = false;