Add swingmusic-mobile submodule to replace Android app

- Updated .gitmodules to include mobile app submodule
- Added swingmusic_mobile directory with Flutter app
- Mobile app will now be built in unified release workflow

swingmusic_mobile/lib/main.dart

@@ -0,0 +1,43 @@
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+import 'features/home/home_screen.dart';
+import 'features/library/library_screen.dart';
+import 'features/player/enhanced_player_screen_new.dart';
+import 'features/search/search_screen.dart';
+import 'features/playlists/playlists_screen.dart';
+import 'features/settings/settings_screen.dart';
+import 'features/auth/enhanced_auth_screen.dart';
+import 'features/analytics/analytics_screen.dart';
+import 'shared/providers/audio_provider.dart';
+import 'shared/providers/auth_provider.dart';
+import 'shared/providers/enhanced_library_provider.dart';
+import 'shared/routes/app_router.dart';
+import 'shared/widgets/main_navigation.dart';
+import 'core/themes/app_theme.dart';
+
+void main() {
+  runApp(const SwingMusicApp());
+}
+
+class SwingMusicApp extends StatelessWidget {
+  const SwingMusicApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MultiProvider(
+      providers: [
+        ChangeNotifierProvider(create: (_) => AudioProvider()),
+        ChangeNotifierProvider(create: (_) => AuthProvider()),
+        ChangeNotifierProvider(create: (_) => EnhancedLibraryProvider()),
+      ],
+      child: MaterialApp.router(
+        title: 'SwingMusic',
+        theme: AppTheme.lightTheme,
+        darkTheme: AppTheme.darkTheme,
+        themeMode: ThemeMode.system,
+        routerConfig: AppRouter.router,
+        debugShowCheckedModeBanner: false,
+      ),
+    );
+  }
+}