feat: use custom FFmpeg AAR for Android, reduce APK size

- Replace ffmpeg_kit_flutter plugin with custom AAR (arm64 + arm7a only)
- Add MethodChannel bridge for FFmpeg in MainActivity
- Create separate pubspec_ios.yaml for iOS builds with ffmpeg_kit plugin
- Update GitHub workflow to swap pubspec for iOS builds
- Reduces Android APK size by ~50MB

pubspec_ios.yaml

@@ -0,0 +1,82 @@
+name: spotiflac_android
+description: Download Spotify tracks in FLAC from Tidal, Qobuz & Amazon Music
+publish_to: 'none'
+version: 2.0.7+37
+
+environment:
+  sdk: ^3.10.0
+
+dependencies:
+  flutter:
+    sdk: flutter
+  
+  # State Management
+  flutter_riverpod: ^3.1.0
+  riverpod_annotation: ^4.0.0
+  
+  # Navigation
+  go_router: ^17.0.1
+  
+  # Storage & Persistence
+  shared_preferences: ^2.5.3
+  path_provider: ^2.1.5
+  
+  # HTTP & Network
+  http: ^1.4.0
+  dio: ^5.8.0
+  
+  # UI Components
+  cupertino_icons: ^1.0.8
+  cached_network_image: ^3.4.1
+  flutter_svg: ^2.1.0
+  
+  # Material Expressive 3 / Dynamic Color
+  dynamic_color: ^1.7.0
+  material_color_utilities: ^0.11.1
+  
+  # Permissions
+  permission_handler: ^12.0.1
+  
+  # File Picker
+  file_picker: ^10.3.0
+  
+  # JSON Serialization
+  json_annotation: ^4.9.0
+  
+  # Utils
+  url_launcher: ^6.3.1
+  device_info_plus: ^12.3.0
+  share_plus: ^12.0.1
+  receive_sharing_intent: ^1.8.1
+  logger: ^2.5.0
+  
+  # FFmpeg for iOS (uses plugin, Android uses custom AAR)
+  ffmpeg_kit_flutter_new_audio: ^2.0.0
+  open_filex: ^4.7.0
+  
+  # Notifications
+  flutter_local_notifications: ^19.0.0
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  flutter_lints: ^6.0.0
+  build_runner: ^2.10.4
+  riverpod_generator: ^4.0.0
+  json_serializable: ^6.11.2
+  flutter_launcher_icons: ^0.14.3
+
+flutter_launcher_icons:
+  android: true
+  ios: true
+  image_path: "icon.png"
+  adaptive_icon_background: "#1a1a2e"
+  adaptive_icon_foreground: "icon.png"
+  ios_content_mode: scaleAspectFill
+  remove_alpha_ios: true
+
+flutter:
+  uses-material-design: true
+  
+  assets:
+    - assets/images/