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_de.dart

@@ -847,4 +847,49 @@ class AppLocalizationsDe extends AppLocalizations {
   String playerRejoined(String name) {
     return '$name ist zurück im Spiel';
   }
+
+  @override
+  String get leaveGameTitle => 'Spiel wirklich verlassen?';
+
+  @override
+  String get leaveGameSingleDevice =>
+      'Das laufende Spiel geht verloren und lässt sich nicht wiederherstellen.';
+
+  @override
+  String get leaveGameHost =>
+      'Du bist der Host: Wenn du gehst, endet das Spiel für alle.';
+
+  @override
+  String get leaveGameClient =>
+      'Du verlässt das Spiel. Du kannst zurückkommen, solange der Host es offen hält.';
+
+  @override
+  String get stayInGame => 'Weiterspielen';
+
+  @override
+  String get permissionsNeededTitle => 'Berechtigungen erforderlich';
+
+  @override
+  String get permissionsNeededBody => 'Für den Mehrspielermodus brauchen wir:';
+
+  @override
+  String get openAppSettingsQuestion => 'Die App-Einstellungen öffnen?';
+
+  @override
+  String get openSettings => 'Einstellungen öffnen';
+
+  @override
+  String get permissionLocation => 'Standort';
+
+  @override
+  String get permissionBluetoothAdvertise => 'Bluetooth (sichtbar machen)';
+
+  @override
+  String get permissionBluetoothConnect => 'Bluetooth (verbinden)';
+
+  @override
+  String get permissionBluetoothScan => 'Bluetooth (suchen)';
+
+  @override
+  String get permissionNearbyWifi => 'Wi-Fi in der Nähe';
 }