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

test/widget_test.dart

@@ -0,0 +1,11 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:rra_app/main.dart';
+
+void main() {
+  testWidgets('Map page shows route builder label', (WidgetTester tester) async {
+    await tester.pumpWidget(const MyApp());
+    await tester.pumpAndSettle();
+
+    expect(find.text('London Route Builder'), findsOneWidget);
+  });
+}