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/add_subscription/add_subscription_save_button.dart

@@ -0,0 +1,52 @@
+import 'package:flutter/material.dart';
+import '../../controllers/add_subscription_controller.dart';
+import '../common/buttons/primary_button.dart';
+
+/// 구독 추가 화면의 저장 버튼
+class AddSubscriptionSaveButton extends StatelessWidget {
+  final AddSubscriptionController controller;
+  final Animation<double> fadeAnimation;
+  final Animation<Offset> slideAnimation;
+  final Function setState;
+
+  const AddSubscriptionSaveButton({
+    super.key,
+    required this.controller,
+    required this.fadeAnimation,
+    required this.slideAnimation,
+    required this.setState,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return FadeTransition(
+      opacity: Tween<double>(begin: 0.0, end: 1.0).animate(
+        CurvedAnimation(
+          parent: controller.animationController!,
+          curve: const Interval(0.6, 1.0, curve: Curves.easeIn),
+        ),
+      ),
+      child: SlideTransition(
+        position: Tween<Offset>(
+          begin: const Offset(0.0, 0.6),
+          end: Offset.zero,
+        ).animate(CurvedAnimation(
+          parent: controller.animationController!,
+          curve: const Interval(0.6, 1.0, curve: Curves.easeOutCubic),
+        )),
+        child: Padding(
+          padding: const EdgeInsets.only(bottom: 80),
+          child: PrimaryButton(
+            text: '구독 추가하기',
+            icon: Icons.add_circle_outline,
+            onPressed: controller.isLoading 
+                ? null 
+                : () => controller.saveSubscription(setState: setState),
+            isLoading: controller.isLoading,
+            backgroundColor: const Color(0xFF3B82F6),
+          ),
+        ),
+      ),
+    );
+  }
+}