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.dart

@@ -1634,6 +1634,90 @@ abstract class AppLocalizations {
   /// In es, this message translates to:
   /// **'{name} ha vuelto a la partida'**
   String playerRejoined(String name);
+
+  /// No description provided for @leaveGameTitle.
+  ///
+  /// In es, this message translates to:
+  /// **'¿Salir de la partida?'**
+  String get leaveGameTitle;
+
+  /// No description provided for @leaveGameSingleDevice.
+  ///
+  /// In es, this message translates to:
+  /// **'Se perderá la partida en curso y no podrás recuperarla.'**
+  String get leaveGameSingleDevice;
+
+  /// No description provided for @leaveGameHost.
+  ///
+  /// In es, this message translates to:
+  /// **'Eres el anfitrión: si sales, la partida termina para todos los jugadores.'**
+  String get leaveGameHost;
+
+  /// No description provided for @leaveGameClient.
+  ///
+  /// In es, this message translates to:
+  /// **'Saldrás de la partida. Podrás volver mientras el anfitrión la mantenga abierta.'**
+  String get leaveGameClient;
+
+  /// No description provided for @stayInGame.
+  ///
+  /// In es, this message translates to:
+  /// **'Seguir jugando'**
+  String get stayInGame;
+
+  /// No description provided for @permissionsNeededTitle.
+  ///
+  /// In es, this message translates to:
+  /// **'Permisos necesarios'**
+  String get permissionsNeededTitle;
+
+  /// No description provided for @permissionsNeededBody.
+  ///
+  /// In es, this message translates to:
+  /// **'Para el modo multijugador necesitamos:'**
+  String get permissionsNeededBody;
+
+  /// No description provided for @openAppSettingsQuestion.
+  ///
+  /// In es, this message translates to:
+  /// **'¿Abrir la configuración de la app?'**
+  String get openAppSettingsQuestion;
+
+  /// No description provided for @openSettings.
+  ///
+  /// In es, this message translates to:
+  /// **'Abrir configuración'**
+  String get openSettings;
+
+  /// No description provided for @permissionLocation.
+  ///
+  /// In es, this message translates to:
+  /// **'Ubicación'**
+  String get permissionLocation;
+
+  /// No description provided for @permissionBluetoothAdvertise.
+  ///
+  /// In es, this message translates to:
+  /// **'Bluetooth (anunciar)'**
+  String get permissionBluetoothAdvertise;
+
+  /// No description provided for @permissionBluetoothConnect.
+  ///
+  /// In es, this message translates to:
+  /// **'Bluetooth (conectar)'**
+  String get permissionBluetoothConnect;
+
+  /// No description provided for @permissionBluetoothScan.
+  ///
+  /// In es, this message translates to:
+  /// **'Bluetooth (escanear)'**
+  String get permissionBluetoothScan;
+
+  /// No description provided for @permissionNearbyWifi.
+  ///
+  /// In es, this message translates to:
+  /// **'Wi-Fi cercano'**
+  String get permissionNearbyWifi;
 }
 
 class _AppLocalizationsDelegate