add initial project files for Flutter app with platform-specific configs and basic routing setup

lib/main.dart

@@ -0,0 +1,27 @@
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+import 'package:rra_app/pages/map/page.dart';
+import 'package:rra_app/pages/map/tiles/hive_tile_cache.dart';
+import 'package:shadcn_flutter/shadcn_flutter.dart' as shadcn;
+import 'package:hive_flutter/hive_flutter.dart';
+
+Future<void> main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+  await Hive.initFlutter();
+  await HiveTileCache.init();
+  runApp(const MyApp());
+}
+
+class MyApp extends StatelessWidget {
+  const MyApp({super.key});
+
+  static final GoRouter _router = GoRouter(routes: [MapPage.route]);
+
+  @override
+  Widget build(BuildContext context) {
+    return shadcn.ShadcnApp.router(
+      title: 'RRA App',
+      routerConfig: _router,
+    );
+  }
+}