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/floating_navigation_bar.dart

@@ -1,6 +1,5 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'dart:ui';
 import '../theme/app_colors.dart';
 import 'glassmorphism_card.dart';
 
@@ -62,8 +61,6 @@ class _FloatingNavigationBarState extends State<FloatingNavigationBar>
 
   @override
   Widget build(BuildContext context) {
-    final isDarkMode = Theme.of(context).brightness == Brightness.dark;
-
     return AnimatedBuilder(
       animation: _animation,
       builder: (context, child) {