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_it.arb

@@ -368,5 +368,19 @@
   "reconnecting": "Riconnessione...",
   "reconnectingHint": "Connessione con l'host persa. Il tuo posto nella partita resta riservato.",
   "leaveGame": "Esci dalla partita",
-  "playerRejoined": "{name} è tornato in partita"
+  "playerRejoined": "{name} è tornato in partita",
+  "leaveGameTitle": "Vuoi uscire dalla partita?",
+  "leaveGameSingleDevice": "La partita in corso andrà persa e non potrà essere recuperata.",
+  "leaveGameHost": "Sei l'host: se esci, la partita finisce per tutti i giocatori.",
+  "leaveGameClient": "Uscirai dalla partita. Potrai rientrare finché l'host la tiene aperta.",
+  "stayInGame": "Continua a giocare",
+  "permissionsNeededTitle": "Autorizzazioni necessarie",
+  "permissionsNeededBody": "Per la modalità multigiocatore servono:",
+  "openAppSettingsQuestion": "Vuoi aprire le impostazioni dell'app?",
+  "openSettings": "Apri impostazioni",
+  "permissionLocation": "Posizione",
+  "permissionBluetoothAdvertise": "Bluetooth (annuncio)",
+  "permissionBluetoothConnect": "Bluetooth (connessione)",
+  "permissionBluetoothScan": "Bluetooth (scansione)",
+  "permissionNearbyWifi": "Wi-Fi nelle vicinanze"
 }