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.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": "至少选择 3 名用户才能开始。",
+  "hostPhoneMustSelectUser": "房主的手机必须至少选择一名用户。",
+  "roomNoLongerInLobby": "房间已不在等候大厅。",
+  "completeUserSelectionToStart": "完成用户选择后才能开始。",
+  "preparingSecureRoom": "正在准备安全房间",
+  "searchingNearbyBluetoothGames": "正在通过蓝牙搜索附近的游戏",
+  "tapToJoin": "点击加入",
+  "bluetoothLocationPermissionsRequired": "搜索游戏需要蓝牙和定位权限。",
+  "bluetoothLocationPermissionsShort": "需要蓝牙和定位权限",
+  "couldNotStartSearch": "无法开始搜索。请检查蓝牙和定位。",
+  "couldNotConnectToHost": "无法连接到 {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": "在这台设备上游戏",
+  "singleDeviceDescription": "适合大家传着手机一起玩。设置快速直接。",
+  "multiDeviceSubtitle": "每位玩家用自己的手机",
+  "multiDeviceDescription": "创建高级房间，分享二维码，并在大厅管理用户。",
+  "singleDeviceGameLabel": "本机游戏",
+  "multiDeviceGameLabel": "多设备游戏",
+  "mainDeviceUser": "本机主用户",
+  "couldNotCreateRoom": "无法创建房间。请检查蓝牙。",
+  "cannotStartWithReason": "无法开始：{reason}",
+  "invalidRoom": "无效的房间",
   "defaultPlayerName": "玩家",
   "play": "开始",
   "history": "历史",
@@ -368,5 +368,19 @@
   "reconnecting": "正在重新连接…",
   "reconnectingHint": "与房主的连接已断开。你在游戏中的位置仍为你保留。",
   "leaveGame": "退出游戏",
-  "playerRejoined": "{name} 已重新加入游戏"
+  "playerRejoined": "{name} 已重新加入游戏",
+  "leaveGameTitle": "要退出游戏吗？",
+  "leaveGameSingleDevice": "正在进行的游戏将会丢失，且无法恢复。",
+  "leaveGameHost": "你是房主：一旦退出，所有玩家的游戏都会结束。",
+  "leaveGameClient": "你将退出这局游戏。只要房主还开着，你随时可以回来。",
+  "stayInGame": "继续游戏",
+  "permissionsNeededTitle": "需要权限",
+  "permissionsNeededBody": "多人游戏模式需要以下权限：",
+  "openAppSettingsQuestion": "要打开应用设置吗？",
+  "openSettings": "打开设置",
+  "permissionLocation": "定位",
+  "permissionBluetoothAdvertise": "蓝牙（广播）",
+  "permissionBluetoothConnect": "蓝牙（连接）",
+  "permissionBluetoothScan": "蓝牙（扫描）",
+  "permissionNearbyWifi": "附近的 Wi-Fi"
 }