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/theme/adaptive_theme.dart

@@ -13,7 +13,7 @@ class AdaptiveTheme {
     return ThemeData(
       useMaterial3: true,
       brightness: Brightness.dark,
-      colorScheme: ColorScheme.dark(
+      colorScheme: const ColorScheme.dark(
         primary: AppColors.primaryColor,
         onPrimary: Colors.white,
         secondary: AppColors.secondaryColor,
@@ -134,11 +134,11 @@ class AdaptiveTheme {
         ),
         focusedBorder: OutlineInputBorder(
           borderRadius: BorderRadius.circular(12),
-          borderSide: BorderSide(color: AppColors.primaryColor, width: 1.5),
+          borderSide: const BorderSide(color: AppColors.primaryColor, width: 1.5),
         ),
         errorBorder: OutlineInputBorder(
           borderRadius: BorderRadius.circular(12),
-          borderSide: BorderSide(color: AppColors.dangerColor, width: 1),
+          borderSide: const BorderSide(color: AppColors.dangerColor, width: 1),
         ),
         labelStyle: TextStyle(
           color: Colors.white.withValues(alpha: 0.7),