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/generated/app_localizations_ja.dart

@@ -645,84 +645,76 @@ class AppLocalizationsJa extends AppLocalizations {
   String get delete => '削除';
 
   @override
-  String get selectAtLeastThreeUsersToStart =>
-      'Select at least 3 users to start.';
+  String get selectAtLeastThreeUsersToStart => '開始するには3人以上のユーザーを選んでください。';
 
   @override
-  String get hostPhoneMustSelectUser =>
-      'The host phone must select at least one user.';
+  String get hostPhoneMustSelectUser => 'ホストの端末は少なくとも1人のユーザーを選ぶ必要があります。';
 
   @override
-  String get roomNoLongerInLobby => 'The room is no longer in the lobby.';
+  String get roomNoLongerInLobby => 'ルームはすでにロビーにありません。';
 
   @override
-  String get completeUserSelectionToStart =>
-      'Complete user selection to start.';
+  String get completeUserSelectionToStart => '開始するにはユーザーの選択を完了してください。';
 
   @override
-  String get preparingSecureRoom => 'Preparing the secure room';
+  String get preparingSecureRoom => '安全なルームを準備しています';
 
   @override
-  String get searchingNearbyBluetoothGames =>
-      'Searching nearby games over Bluetooth';
+  String get searchingNearbyBluetoothGames => 'Bluetoothで近くのゲームを検索しています';
 
   @override
-  String get tapToJoin => 'Tap to join';
+  String get tapToJoin => 'タップして参加';
 
   @override
   String get bluetoothLocationPermissionsRequired =>
-      'Bluetooth and location permissions are required to search for games.';
+      'ゲームを検索するにはBluetoothと位置情報の許可が必要です。';
 
   @override
-  String get bluetoothLocationPermissionsShort =>
-      'Bluetooth and location permissions are required';
+  String get bluetoothLocationPermissionsShort => 'Bluetoothと位置情報の許可が必要です';
 
   @override
-  String get couldNotStartSearch =>
-      'Could not start the search. Check Bluetooth and location.';
+  String get couldNotStartSearch => '検索を開始できませんでした。Bluetoothと位置情報を確認してください。';
 
   @override
   String couldNotConnectToHost(String host) {
-    return 'Could not connect to $host';
+    return '$host に接続できませんでした';
   }
 
   @override
   String get room => 'ルーム';
 
   @override
-  String get singleDeviceSubtitle => 'Game on this device';
+  String get singleDeviceSubtitle => 'この端末でプレイ';
 
   @override
-  String get singleDeviceDescription =>
-      'Ideal for playing together by passing the phone around. Fast, direct setup.';
+  String get singleDeviceDescription => '端末を回しながらみんなで遊ぶのに最適。設定はすばやく簡単。';
 
   @override
-  String get multiDeviceSubtitle => 'Each player on their phone';
+  String get multiDeviceSubtitle => 'プレイヤーごとに自分の端末で';
 
   @override
   String get multiDeviceDescription =>
-      'Create a premium room, share the QR code and manage users from the lobby.';
+      'プレミアムなルームを作り、QRコードを共有し、ロビーからユーザーを管理します。';
 
   @override
-  String get singleDeviceGameLabel => 'Game on this device';
+  String get singleDeviceGameLabel => 'この端末でのゲーム';
 
   @override
-  String get multiDeviceGameLabel => 'Multi-device game';
+  String get multiDeviceGameLabel => 'マルチデバイスのゲーム';
 
   @override
-  String get mainDeviceUser => 'Main device user';
+  String get mainDeviceUser => 'この端末のメインユーザー';
 
   @override
-  String get couldNotCreateRoom =>
-      'Could not create the room. Check Bluetooth.';
+  String get couldNotCreateRoom => 'ルームを作成できませんでした。Bluetoothを確認してください。';
 
   @override
   String cannotStartWithReason(String reason) {
-    return 'Cannot start: $reason';
+    return '開始できません: $reason';
   }
 
   @override
-  String get invalidRoom => 'invalid room';
+  String get invalidRoom => '無効なルーム';
 
   @override
   String get defaultPlayerName => 'プレイヤー';
@@ -831,4 +823,46 @@ class AppLocalizationsJa extends AppLocalizations {
   String playerRejoined(String name) {
     return '$name がゲームに復帰しました';
   }
+
+  @override
+  String get leaveGameTitle => 'ゲームから退出しますか？';
+
+  @override
+  String get leaveGameSingleDevice => '進行中のゲームは失われ、元に戻せません。';
+
+  @override
+  String get leaveGameHost => 'あなたはホストです。退出すると全員のゲームが終了します。';
+
+  @override
+  String get leaveGameClient => 'ゲームから退出します。ホストが開いている間は戻れます。';
+
+  @override
+  String get stayInGame => 'ゲームを続ける';
+
+  @override
+  String get permissionsNeededTitle => '必要な権限';
+
+  @override
+  String get permissionsNeededBody => 'マルチプレイには次の権限が必要です：';
+
+  @override
+  String get openAppSettingsQuestion => 'アプリの設定を開きますか？';
+
+  @override
+  String get openSettings => '設定を開く';
+
+  @override
+  String get permissionLocation => '位置情報';
+
+  @override
+  String get permissionBluetoothAdvertise => 'Bluetooth（アドバタイズ）';
+
+  @override
+  String get permissionBluetoothConnect => 'Bluetooth（接続）';
+
+  @override
+  String get permissionBluetoothScan => 'Bluetooth（スキャン）';
+
+  @override
+  String get permissionNearbyWifi => '近くのWi-Fi';
 }