feat(frontend): App 路由集成 + 木纹风格 CSS

App.tsx 添加 menu/game/replay 三页面路由切换，MainMenu 新增
onReplayStart 属性区分对局与回放入口。App.css 实现经典木纹
视觉风格（深棕底色、米黄文字、皮革纹理按钮），index.css 基础
重置。修复 tsconfig 中 erasableSyntaxOnly 无效选项并安装
@types/node。

src/App.tsx

@@ -1,8 +1,26 @@
+import { useState } from 'react';
+import MainMenu from './components/menu/MainMenu';
+import GameView from './components/game/GameView';
+import ReplayView from './components/replay/ReplayView';
+import './App.css';
+
+type Page = 'menu' | 'game' | 'replay';
+
 function App() {
+  const [page, setPage] = useState<Page>('menu');
+
+  const handleGameStart = () => setPage('game');
+  const handleReplayStart = () => setPage('replay');
+  const handleBackToMenu = () => setPage('menu');
+
+  if (page === 'game') return <GameView onBackToMenu={handleBackToMenu} />;
+  if (page === 'replay') return <ReplayView onBackToMenu={handleBackToMenu} />;
+
   return (
-    <div className="app">
-      <h1>五子棋 v2.0</h1>
-    </div>
+    <MainMenu
+      onGameStart={handleGameStart}
+      onReplayStart={handleReplayStart}
+    />
   );
 }