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/pantallas/pantalla_adivinanza.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import '../tema/dialogo_confirmacion.dart';
 import 'package:farolero/l10n/generated/app_localizations.dart';
 import 'package:provider/provider.dart';
 import '../estado/estado_juego.dart';
@@ -53,31 +54,34 @@ class _PantallaAdivinanzaState extends State<PantallaAdivinanza> {
     final partida = estado.partida;
     if (partida == null) return const SizedBox.shrink();
 
-    return Scaffold(
-      appBar: AppBar(
-        title: Text(l10n.impostorGuessTitle),
-        automaticallyImplyLeading: false,
-      ),
-      body: FondoFarolero(
-        intenso: true,
-        child: SafeArea(
-          child: Center(
-            child: SingleChildScrollView(
-              padding: const EdgeInsets.all(24),
-              child: Column(
-                mainAxisAlignment: MainAxisAlignment.center,
-                children: [
-                  const ArteGameplayFarolero.fase(height: 132),
-                  const SizedBox(height: 12),
-                  TarjetaFaseFarolero(
-                    icono: Icons.theater_comedy,
-                    assetIconPath: 'assets/ui/generated/actions/action_impostor_mask.webp',
-                    titulo: l10n.impostorCanGuess,
-                    subtitulo: l10n.ifCorrectImpostorsWin,
-                    color: TemaApp.colorAcento,
-                    child: _buildContenido(context, l10n, estado, partida.palabraSecreta),
-                  ),
-                ],
+    return GuardiaSalidaPartida(
+      contexto: ContextoSalida.unDispositivo,
+      child: Scaffold(
+        appBar: AppBar(
+          title: Text(l10n.impostorGuessTitle),
+          automaticallyImplyLeading: false,
+        ),
+        body: FondoFarolero(
+          intenso: true,
+          child: SafeArea(
+            child: Center(
+              child: SingleChildScrollView(
+                padding: const EdgeInsets.all(24),
+                child: Column(
+                  mainAxisAlignment: MainAxisAlignment.center,
+                  children: [
+                    const ArteGameplayFarolero.fase(height: 132),
+                    const SizedBox(height: 12),
+                    TarjetaFaseFarolero(
+                      icono: Icons.theater_comedy,
+                      assetIconPath: 'assets/ui/generated/actions/action_impostor_mask.webp',
+                      titulo: l10n.impostorCanGuess,
+                      subtitulo: l10n.ifCorrectImpostorsWin,
+                      color: TemaApp.colorAcento,
+                      child: _buildContenido(context, l10n, estado, partida.palabraSecreta),
+                    ),
+                  ],
+                ),
               ),
             ),
           ),