feat: confirm before leaving a game, and fix untranslated strings

Exit confirmation
- A dialog in the app's own style now guards every in-game screen. The safe
  action is the prominent one, so a stray tap keeps you in the game.
- Eleven screens covered, against both the system back gesture and the close
  buttons. The message adapts: a single-device game is lost, a host ends it
  for everyone, a client can rejoin.
- The two screens the host also opens from the manager take a flag so that
  back there just closes them instead of offering to quit.

Translations
- 21 keys were still holding the English text in Arabic, Basque, Hindi,
  Japanese, Korean, Dutch, Polish, Russian, Turkish and both Chinese
  variants: 231 strings, covering the whole multi-device flow, permissions
  and the mode picker. Nothing failed, the app just showed English.
- The permissions dialog was hardcoded in Spanish; it is localized now.
- Portuguese used Spanish gerunds where pt-PT takes "a + infinitive".

Checked what looked untranslated but is not: Animals and Notes are correct
Catalan, Configuration and Vibration correct French, Version correct German.
Those are whitelisted in the new test rather than silently rewritten.

l10n_cobertura_test guards all of it: no missing or orphan keys, no empty
values, no English left outside the whitelist, and placeholders preserved.

lib/l10n/app_zh_TW.arb

@@ -246,28 +246,28 @@
   "release": "释放",
   "select": "选择",
   "delete": "删除",
-  "selectAtLeastThreeUsersToStart": "Select at least 3 users to start.",
-  "hostPhoneMustSelectUser": "The host phone must select at least one user.",
-  "roomNoLongerInLobby": "The room is no longer in the lobby.",
-  "completeUserSelectionToStart": "Complete user selection to start.",
-  "preparingSecureRoom": "Preparing the secure room",
-  "searchingNearbyBluetoothGames": "Searching nearby games over Bluetooth",
-  "tapToJoin": "Tap to join",
-  "bluetoothLocationPermissionsRequired": "Bluetooth and location permissions are required to search for games.",
-  "bluetoothLocationPermissionsShort": "Bluetooth and location permissions are required",
-  "couldNotStartSearch": "Could not start the search. Check Bluetooth and location.",
-  "couldNotConnectToHost": "Could not connect to {host}",
+  "selectAtLeastThreeUsersToStart": "至少選擇 3 名使用者才能開始。",
+  "hostPhoneMustSelectUser": "房主的手機必須至少選擇一名使用者。",
+  "roomNoLongerInLobby": "房間已不在等候大廳。",
+  "completeUserSelectionToStart": "完成使用者選擇後才能開始。",
+  "preparingSecureRoom": "正在準備安全房間",
+  "searchingNearbyBluetoothGames": "正在透過藍牙搜尋附近的遊戲",
+  "tapToJoin": "點擊加入",
+  "bluetoothLocationPermissionsRequired": "搜尋遊戲需要藍牙和定位權限。",
+  "bluetoothLocationPermissionsShort": "需要藍牙和定位權限",
+  "couldNotStartSearch": "無法開始搜尋。請檢查藍牙和定位。",
+  "couldNotConnectToHost": "無法連線到 {host}",
   "room": "房间",
-  "singleDeviceSubtitle": "Game on this device",
-  "singleDeviceDescription": "Ideal for playing together by passing the phone around. Fast, direct setup.",
-  "multiDeviceSubtitle": "Each player on their phone",
-  "multiDeviceDescription": "Create a premium room, share the QR code and manage users from the lobby.",
-  "singleDeviceGameLabel": "Game on this device",
-  "multiDeviceGameLabel": "Multi-device game",
-  "mainDeviceUser": "Main device user",
-  "couldNotCreateRoom": "Could not create the room. Check Bluetooth.",
-  "cannotStartWithReason": "Cannot start: {reason}",
-  "invalidRoom": "invalid room",
+  "singleDeviceSubtitle": "在這台裝置上遊戲",
+  "singleDeviceDescription": "適合大家傳著手機一起玩。設定快速直接。",
+  "multiDeviceSubtitle": "每位玩家用自己的手機",
+  "multiDeviceDescription": "建立高級房間，分享 QR Code，並在大廳管理使用者。",
+  "singleDeviceGameLabel": "本機遊戲",
+  "multiDeviceGameLabel": "多裝置遊戲",
+  "mainDeviceUser": "本機主要使用者",
+  "couldNotCreateRoom": "無法建立房間。請檢查藍牙。",
+  "cannotStartWithReason": "無法開始：{reason}",
+  "invalidRoom": "無效的房間",
   "defaultPlayerName": "玩家",
   "play": "開始",
   "history": "紀錄",
@@ -368,5 +368,19 @@
   "reconnecting": "正在重新連線…",
   "reconnectingHint": "與房主的連線已中斷。你在遊戲中的位置仍為你保留。",
   "leaveGame": "退出遊戲",
-  "playerRejoined": "{name} 已重新加入遊戲"
+  "playerRejoined": "{name} 已重新加入遊戲",
+  "leaveGameTitle": "要退出遊戲嗎？",
+  "leaveGameSingleDevice": "正在進行的遊戲將會遺失，且無法復原。",
+  "leaveGameHost": "你是房主：一旦退出，所有玩家的遊戲都會結束。",
+  "leaveGameClient": "你將退出這局遊戲。只要房主還開著，你隨時可以回來。",
+  "stayInGame": "繼續遊戲",
+  "permissionsNeededTitle": "需要權限",
+  "permissionsNeededBody": "多人遊戲模式需要以下權限：",
+  "openAppSettingsQuestion": "要開啟應用程式設定嗎？",
+  "openSettings": "開啟設定",
+  "permissionLocation": "定位",
+  "permissionBluetoothAdvertise": "藍牙（廣播）",
+  "permissionBluetoothConnect": "藍牙（連線）",
+  "permissionBluetoothScan": "藍牙（掃描）",
+  "permissionNearbyWifi": "附近的 Wi-Fi"
 }