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/screens/app_lock_screen.dart

@@ -38,7 +38,7 @@ class AppLockScreen extends StatelessWidget {
               onPressed: () async {
                 final appLock = context.read<AppLockProvider>();
                 final success = await appLock.authenticate();
-                if (!success) {
+                if (!success && context.mounted) {
                   ScaffoldMessenger.of(context).showSnackBar(
                     const SnackBar(
                       content: Text('인증에 실패했습니다. 다시 시도해주세요.'),