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/common/buttons/primary_button.dart

@@ -0,0 +1,112 @@
+import 'package:flutter/material.dart';
+
+/// 주요 액션에 사용되는 Primary 버튼
+/// 저장, 추가, 확인 등의 주요 액션에 사용됩니다.
+class PrimaryButton extends StatefulWidget {
+  final String text;
+  final VoidCallback? onPressed;
+  final bool isLoading;
+  final IconData? icon;
+  final double? width;
+  final double height;
+  final Color? backgroundColor;
+  final Color? foregroundColor;
+  final double fontSize;
+  final EdgeInsetsGeometry? padding;
+  final double borderRadius;
+  final bool enableHoverEffect;
+
+  const PrimaryButton({
+    super.key,
+    required this.text,
+    this.onPressed,
+    this.isLoading = false,
+    this.icon,
+    this.width,
+    this.height = 60,
+    this.backgroundColor,
+    this.foregroundColor,
+    this.fontSize = 18,
+    this.padding,
+    this.borderRadius = 16,
+    this.enableHoverEffect = true,
+  });
+
+  @override
+  State<PrimaryButton> createState() => _PrimaryButtonState();
+}
+
+class _PrimaryButtonState extends State<PrimaryButton> {
+  bool _isHovered = false;
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final effectiveBackgroundColor = widget.backgroundColor ?? theme.primaryColor;
+    final effectiveForegroundColor = widget.foregroundColor ?? Colors.white;
+
+    Widget button = AnimatedContainer(
+      duration: const Duration(milliseconds: 200),
+      width: widget.width ?? double.infinity,
+      height: widget.height,
+      transform: widget.enableHoverEffect && _isHovered
+          ? (Matrix4.identity()..scale(1.02))
+          : Matrix4.identity(),
+      child: ElevatedButton(
+        onPressed: widget.isLoading ? null : widget.onPressed,
+        style: ElevatedButton.styleFrom(
+          backgroundColor: effectiveBackgroundColor,
+          foregroundColor: effectiveForegroundColor,
+          shape: RoundedRectangleBorder(
+            borderRadius: BorderRadius.circular(widget.borderRadius),
+          ),
+          padding: widget.padding ?? const EdgeInsets.symmetric(vertical: 16),
+          elevation: widget.enableHoverEffect && _isHovered ? 8 : 4,
+          shadowColor: effectiveBackgroundColor.withOpacity(0.5),
+          disabledBackgroundColor: effectiveBackgroundColor.withOpacity(0.6),
+        ),
+        child: widget.isLoading
+            ? SizedBox(
+                width: 24,
+                height: 24,
+                child: CircularProgressIndicator(
+                  strokeWidth: 2.5,
+                  color: effectiveForegroundColor,
+                ),
+              )
+            : Row(
+                mainAxisAlignment: MainAxisAlignment.center,
+                mainAxisSize: MainAxisSize.min,
+                children: [
+                  if (widget.icon != null) ...[
+                    Icon(
+                      widget.icon,
+                      color: effectiveForegroundColor,
+                      size: _isHovered ? 24 : 20,
+                    ),
+                    const SizedBox(width: 8),
+                  ],
+                  Text(
+                    widget.text,
+                    style: TextStyle(
+                      fontSize: widget.fontSize,
+                      fontWeight: FontWeight.w600,
+                      color: effectiveForegroundColor,
+                    ),
+                  ),
+                ],
+              ),
+      ),
+    );
+
+    if (widget.enableHoverEffect) {
+      return MouseRegion(
+        onEnter: (_) => setState(() => _isHovered = true),
+        onExit: (_) => setState(() => _isHovered = false),
+        child: button,
+      );
+    }
+
+    return button;
+  }
+}