Scaffold Block Seasons Flutter app

flutter create (com.airkjw.blockseasons, iOS+Android), Riverpod,
shared_preferences, audioplayers, gen-l10n EN/KO wiring, app shell
with Home -> Game placeholder.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/ui/screens/game_screen.dart

@@ -0,0 +1,17 @@
+import 'package:flutter/material.dart';
+
+import '../../l10n/gen/app_localizations.dart';
+
+/// Placeholder until the board UI lands in Phase 2.
+class GameScreen extends StatelessWidget {
+  const GameScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context)!;
+    return Scaffold(
+      appBar: AppBar(title: Text(l10n.appTitle)),
+      body: Center(child: Text(l10n.comingSoon)),
+    );
+  }
+}