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_nl.arb

@@ -246,28 +246,28 @@
   "release": "Vrijgeven",
   "select": "Selecteren",
   "delete": "Verwijderen",
-  "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": "Selecteer minstens 3 gebruikers om te starten.",
+  "hostPhoneMustSelectUser": "De host-telefoon moet minstens één gebruiker selecteren.",
+  "roomNoLongerInLobby": "De ruimte is niet meer in de lobby.",
+  "completeUserSelectionToStart": "Voltooi de gebruikersselectie om te starten.",
+  "preparingSecureRoom": "Beveiligde ruimte voorbereiden",
+  "searchingNearbyBluetoothGames": "Zoeken naar spellen in de buurt via Bluetooth",
+  "tapToJoin": "Tik om deel te nemen",
+  "bluetoothLocationPermissionsRequired": "Bluetooth- en locatietoestemming zijn nodig om spellen te zoeken.",
+  "bluetoothLocationPermissionsShort": "Bluetooth- en locatietoestemming zijn nodig",
+  "couldNotStartSearch": "Kon het zoeken niet starten. Controleer Bluetooth en locatie.",
+  "couldNotConnectToHost": "Kon geen verbinding maken met {host}",
   "room": "Kamer",
-  "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": "Spel op dit toestel",
+  "singleDeviceDescription": "Ideaal om samen te spelen door de telefoon door te geven. Snel en direct ingesteld.",
+  "multiDeviceSubtitle": "Elke speler op zijn eigen telefoon",
+  "multiDeviceDescription": "Maak een premium ruimte, deel de QR-code en beheer gebruikers vanuit de lobby.",
+  "singleDeviceGameLabel": "Spel op dit toestel",
+  "multiDeviceGameLabel": "Spel met meerdere toestellen",
+  "mainDeviceUser": "Hoofdgebruiker van dit toestel",
+  "couldNotCreateRoom": "Kon de ruimte niet aanmaken. Controleer Bluetooth.",
+  "cannotStartWithReason": "Kan niet starten: {reason}",
+  "invalidRoom": "ongeldige ruimte",
   "defaultPlayerName": "Speler",
   "play": "Spelen",
   "history": "Geschiedenis",
@@ -368,5 +368,19 @@
   "reconnecting": "Opnieuw verbinden...",
   "reconnectingHint": "Verbinding met de host verbroken. Je plek in het spel blijft behouden.",
   "leaveGame": "Spel verlaten",
-  "playerRejoined": "{name} is terug in het spel"
+  "playerRejoined": "{name} is terug in het spel",
+  "leaveGameTitle": "Het spel verlaten?",
+  "leaveGameSingleDevice": "Het lopende spel gaat verloren en kan niet worden hersteld.",
+  "leaveGameHost": "Jij bent de host: als je weggaat, eindigt het spel voor iedereen.",
+  "leaveGameClient": "Je verlaat het spel. Je kunt terugkomen zolang de host het openhoudt.",
+  "stayInGame": "Verder spelen",
+  "permissionsNeededTitle": "Toestemmingen nodig",
+  "permissionsNeededBody": "Voor de multiplayermodus hebben we nodig:",
+  "openAppSettingsQuestion": "De app-instellingen openen?",
+  "openSettings": "Instellingen openen",
+  "permissionLocation": "Locatie",
+  "permissionBluetoothAdvertise": "Bluetooth (zichtbaar maken)",
+  "permissionBluetoothConnect": "Bluetooth (verbinden)",
+  "permissionBluetoothScan": "Bluetooth (scannen)",
+  "permissionNearbyWifi": "Wi-Fi in de buurt"
 }