chore: bring flutter client, docs, deploy and tools into monorepo

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

musify_flutter/lib/src/app.dart

@@ -0,0 +1,20 @@
+import 'package:flutter/material.dart';
+
+import 'core/router/app_router.dart';
+import 'core/theme/app_theme.dart';
+
+class MusifyApp extends StatelessWidget {
+  const MusifyApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp.router(
+      title: 'Musify',
+      debugShowCheckedModeBanner: false,
+      theme: AppTheme.light(),
+      darkTheme: AppTheme.dark(),
+      themeMode: ThemeMode.system,
+      routerConfig: appRouter,
+    );
+  }
+}