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/widgets/subscription_list_widget.dart

@@ -1,11 +1,8 @@
 import 'package:flutter/material.dart';
 import '../models/subscription_model.dart';
-import '../widgets/subscription_card.dart';
 import '../widgets/category_header_widget.dart';
 import '../widgets/swipeable_subscription_card.dart';
 import '../widgets/staggered_list_animation.dart';
-import '../screens/detail_screen.dart';
-import '../widgets/animated_page_transitions.dart';
 import '../widgets/app_navigator.dart';
 import 'package:provider/provider.dart';
 import '../providers/subscription_provider.dart';
@@ -62,8 +59,8 @@ class SubscriptionListWidget extends StatelessWidget {
                     itemBuilder: (context, subIndex) {
                       // 각 구독의 지연값 계산 (순차적으로 나타나도록)
                       final delay = 0.05 * subIndex;
-                      final animationBegin = 0.2;
-                      final animationEnd = 1.0;
+                      const animationBegin = 0.2;
+                      const animationEnd = 1.0;
                       final intervalStart = delay;
                       final intervalEnd = intervalStart + 0.4;