本遊戲以 Firebase Realtime Database 同步全班裝置。一次設定即可永久使用 (免費版額度遠超一堂課所需)。 Multiplayer uses Firebase Realtime Database to sync devices across the classroom. One-time setup; free tier covers a full lesson easily.

1. 前往 Firebase Console 建立新專案 (免費) Go to Firebase Console, create a free project
2. 啟用 Realtime Database (測試模式啟動) Enable Realtime Database (start in test mode)
3. 啟用 Authentication → 匿名登入 Enable Authentication → Anonymous sign-in
4. 在「專案設定 → 一般」加入「網頁應用程式」並複製 firebaseConfig In Project Settings → General → Add Web App, copy the firebaseConfig
5. 在本 HTML 檔案搜尋 FIREBASE_CONFIG，貼上你的設定，重新載入 Search this HTML for FIREBASE_CONFIG, paste your config, reload

建議 RTDB 安全規則 (Demo): Suggested RTDB rules (Demo):

{
  "rules": {
    "rooms": {
      "$code": {
        ".read":  "auth != null",
        ".write": "auth != null"
      }
    }
  }
}

⚠ 上述規則僅供 demo;正式部署請加上每房間 host UID 寫入限制及 30 分鐘自動清理。 ⚠ Demo rules only. For production, lock writes to host UID per room + add 30-min auto-cleanup.