feat(i18n): add FR/EN internationalization with in-app language selector

- gen-l10n setup (flutter_localizations, intl, l10n.yaml, ARB en/fr)
- localeProvider (persisted) wired into MaterialApp
- language selector in the System page (alongside the color palette)
- all user-facing strings across screens moved to AppLocalizations

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/presentation/widgets/game_over/game_over_actions.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import '../../../l10n/app_localizations.dart';
 
 /// Boutons d'action de l'écran game over : rejouer ou retourner au Pokédex.
 class GameOverActions extends StatelessWidget {
@@ -9,11 +10,12 @@ class GameOverActions extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final l = AppLocalizations.of(context)!;
     return Column(
       children: [
-        _button(label: "TRY AGAIN", icon: Icons.refresh, color: const Color(0xFF2962FF), onPressed: onTryAgain),
+        _button(label: l.tryAgain, icon: Icons.refresh, color: const Color(0xFF2962FF), onPressed: onTryAgain),
         const SizedBox(height: 16),
-        _button(label: "BACK TO POKEDEX", icon: Icons.menu_book, color: const Color(0xFFA66A00), onPressed: onBack),
+        _button(label: l.backToPokedex, icon: Icons.menu_book, color: const Color(0xFFA66A00), onPressed: onBack),
       ],
     );
   }

lib/presentation/widgets/game_over/game_over_header.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import '../../../l10n/app_localizations.dart';
 import '../pokemon_image.dart';
 
 /// Bloc supérieur de l'écran game over : bannière "GAME OVER", image et nom du Pokémon.
@@ -13,6 +14,7 @@ class GameOverHeader extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final l = AppLocalizations.of(context)!;
     return Container(
       decoration: BoxDecoration(color: _darkRed, border: Border.all(color: _darkRed, width: 4)),
       child: Container(
@@ -24,9 +26,9 @@ class GameOverHeader extends StatelessWidget {
             Container(
               color: _darkRed,
               padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 8),
-              child: const Text(
-                "GAME OVER",
-                style: TextStyle(
+              child: Text(
+                l.gameOver,
+                style: const TextStyle(
                   fontSize: 26,
                   color: Colors.yellow,
                   fontWeight: FontWeight.bold,
@@ -40,7 +42,7 @@ class GameOverHeader extends StatelessWidget {
               SizedBox(height: 140, child: PokemonImage(imageUrl: pokemonImage, fit: BoxFit.contain)),
             const SizedBox(height: 12),
             Text(
-              "It was $pokemonName!",
+              l.itWas(pokemonName),
               textAlign: TextAlign.center,
               style: const TextStyle(
                 fontSize: 22,

lib/presentation/widgets/game_over/game_over_stats.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import '../../../l10n/app_localizations.dart';
 
 /// Rangée de statistiques de fin de partie (STREAK / SEEN / SCORE).
 class GameOverStats extends StatelessWidget {
@@ -10,13 +11,14 @@ class GameOverStats extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final l = AppLocalizations.of(context)!;
     return Row(
       children: [
-        Expanded(child: _StatBox(label: "STREAK", value: streak)),
+        Expanded(child: _StatBox(label: l.statStreak, value: streak)),
         const SizedBox(width: 16),
-        Expanded(child: _StatBox(label: "SEEN", value: seen)),
+        Expanded(child: _StatBox(label: l.statSeen, value: seen)),
         const SizedBox(width: 16),
-        Expanded(child: _StatBox(label: "SCORE", value: score)),
+        Expanded(child: _StatBox(label: l.statScore, value: score)),
       ],
     );
   }