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_app_bar.dart

@@ -0,0 +1,95 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/foundation.dart' show kIsWeb;
+import 'package:font_awesome_flutter/font_awesome_flutter.dart';
+import 'dart:math' as math;
+import '../../controllers/add_subscription_controller.dart';
+
+/// 구독 추가 화면의 App Bar
+class AddSubscriptionAppBar extends StatelessWidget implements PreferredSizeWidget {
+  final AddSubscriptionController controller;
+  final double scrollOffset;
+  final VoidCallback onScanSMS;
+
+  const AddSubscriptionAppBar({
+    super.key,
+    required this.controller,
+    required this.scrollOffset,
+    required this.onScanSMS,
+  });
+
+  @override
+  Size get preferredSize => const Size.fromHeight(60);
+
+  @override
+  Widget build(BuildContext context) {
+    final double appBarOpacity = math.max(0, math.min(1, scrollOffset / 100));
+
+    return Container(
+      decoration: BoxDecoration(
+        color: Colors.white.withOpacity(appBarOpacity),
+        boxShadow: appBarOpacity > 0.6
+            ? [
+                BoxShadow(
+                  color: Colors.black.withOpacity(0.1 * appBarOpacity),
+                  spreadRadius: 1,
+                  blurRadius: 8,
+                  offset: const Offset(0, 4),
+                )
+              ]
+            : null,
+      ),
+      child: SafeArea(
+        child: AppBar(
+          title: Text(
+            '구독 추가',
+            style: TextStyle(
+              fontFamily: 'Montserrat',
+              fontSize: 24,
+              fontWeight: FontWeight.w800,
+              letterSpacing: -0.5,
+              color: const Color(0xFF1E293B),
+              shadows: appBarOpacity > 0.6
+                  ? [
+                      Shadow(
+                        color: Colors.black.withOpacity(0.2),
+                        offset: const Offset(0, 1),
+                        blurRadius: 2,
+                      )
+                    ]
+                  : null,
+            ),
+          ),
+          elevation: 0,
+          backgroundColor: Colors.transparent,
+          actions: [
+            if (!kIsWeb)
+              controller.isLoading
+                  ? const Padding(
+                      padding: EdgeInsets.only(right: 16.0),
+                      child: Center(
+                        child: SizedBox(
+                          width: 24,
+                          height: 24,
+                          child: CircularProgressIndicator(
+                            strokeWidth: 2,
+                            valueColor: AlwaysStoppedAnimation<Color>(
+                                Color(0xFF3B82F6)),
+                          ),
+                        ),
+                      ),
+                    )
+                  : IconButton(
+                      icon: const FaIcon(
+                        FontAwesomeIcons.message,
+                        size: 20,
+                        color: Color(0xFF3B82F6),
+                      ),
+                      onPressed: onScanSMS,
+                      tooltip: 'SMS에서 구독 정보 스캔',
+                    ),
+          ],
+        ),
+      ),
+    );
+  }
+}