fix: ensure notifications use correct channels and dates

lib/controllers/detail_screen_controller.dart

@@ -13,7 +13,6 @@ import '../widgets/dialogs/delete_confirmation_dialog.dart';
 import '../widgets/common/snackbar/app_snackbar.dart';
 import '../l10n/app_localizations.dart';
 import '../utils/billing_date_util.dart';
-import '../utils/business_day_util.dart';
 
 /// DetailScreen의 비즈니스 로직을 관리하는 Controller
 class DetailScreenController extends ChangeNotifier {
@@ -414,8 +413,6 @@ class DetailScreenController extends ChangeNotifier {
         _nextBillingDate.year, _nextBillingDate.month, _nextBillingDate.day);
     var adjustedNext =
         BillingDateUtil.ensureFutureDate(originalDateOnly, _billingCycle);
-    // 주말/고정 공휴일 보정 → 다음 영업일로 이월
-    adjustedNext = BusinessDayUtil.nextBusinessDay(adjustedNext);
     subscription.nextBillingDate = adjustedNext;
     subscription.categoryId = _selectedCategoryId;
     subscription.currency = _currency;