fix: 禁用未完成的网络对战入口，标注开发中

src/components/menu/MainMenu.tsx

@@ -27,7 +27,13 @@ export default function MainMenu({ onGameStart, onReplayStart }: Props) {
       <div className="menu-buttons">
         <button onClick={() => setView('local')}>{t('menu.local_game')}</button>
         <button onClick={() => setView('ai')}>{t('menu.ai_game')}</button>
-        <button onClick={() => setView('online')}>{t('menu.online_game')}</button>
+        <button
+          onClick={() => setView('online')}
+          disabled
+          title={t('menu.online_game_disabled')}
+        >
+          {t('menu.online_game')} (开发中)
+        </button>
         <button onClick={() => setView('replay')}>{t('menu.load_replay')}</button>
       </div>
     </div>

src/i18n/en.json

@@ -4,6 +4,7 @@
     "local_game": "Local 2-Player",
     "ai_game": "VS AI",
     "online_game": "Online",
+    "online_game_disabled": "Online mode is under development",
     "load_replay": "Load Replay",
     "settings": "Settings"
   },

src/i18n/zh-CN.json

@@ -4,6 +4,7 @@
     "local_game": "本地双人",
     "ai_game": "人机对战",
     "online_game": "网络对战",
+    "online_game_disabled": "网络对战功能开发中",
     "load_replay": "加载棋谱",
     "settings": "设置"
   },