Refactor screens to MVC architecture with modular widgets

- Extract business logic from screens into dedicated controllers
- Split large screen files into smaller, reusable widget components
- Add controllers for AddSubscriptionScreen and DetailScreen
- Create modular widgets for subscription and detail features
- Improve code organization and maintainability
- Remove duplicated code and improve reusability

🤖 Generated with [Claude Code](https://claude.ai/code)

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

lib/providers/notification_provider.dart

@@ -1,4 +1,3 @@
-import 'package:flutter/material.dart';
 import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 import 'package:flutter/foundation.dart';
 import '../services/notification_service.dart';

lib/providers/subscription_provider.dart

@@ -4,9 +4,6 @@ import 'package:hive/hive.dart';
 import 'package:uuid/uuid.dart';
 import '../models/subscription_model.dart';
 import '../services/notification_service.dart';
-import 'package:provider/provider.dart';
-import 'notification_provider.dart';
-import '../navigator_key.dart';
 
 class SubscriptionProvider extends ChangeNotifier {
   late Box<SubscriptionModel> _subscriptionBox;
@@ -156,35 +153,6 @@ class SubscriptionProvider extends ChangeNotifier {
     }
   }
 
-  Future<void> _scheduleNotifications() async {
-    final BuildContext? context = navigatorKey.currentContext;
-    if (context == null) return;
-
-    final notificationProvider = Provider.of<NotificationProvider>(
-      context,
-      listen: false,
-    );
-
-    if (!notificationProvider.isEnabled ||
-        !notificationProvider.isPaymentEnabled) {
-      return;
-    }
-
-    for (final subscription in _subscriptions) {
-      final notificationDate = subscription.nextBillingDate.subtract(
-        const Duration(days: 3),
-      );
-
-      if (notificationDate.isAfter(DateTime.now())) {
-        await NotificationService.scheduleNotification(
-          id: subscription.id.hashCode,
-          title: '구독 결제 예정 알림',
-          body: '${subscription.serviceName}의 결제가 3일 후 예정되어 있습니다.',
-          scheduledDate: notificationDate,
-        );
-      }
-    }
-  }
 
   Future<void> clearAllSubscriptions() async {
     _isLoading = true;