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/list/pokedex_count_bar.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import '../../../l10n/app_localizations.dart';
 
 /// Bandeau affichant le nombre de Pokémon découverts sur le total.
 class PokedexCountBar extends StatelessWidget {
@@ -20,8 +21,8 @@ class PokedexCountBar extends StatelessWidget {
             '${caught.toString().padLeft(3, '0')} / $total',
             style: const TextStyle(fontSize: 32, fontWeight: FontWeight.bold),
           ),
-          const Text('POKEMON DISCOVERED',
-              style: TextStyle(fontSize: 14, color: Colors.black54, letterSpacing: 1)),
+          Text(AppLocalizations.of(context)!.pokemonDiscovered,
+              style: const TextStyle(fontSize: 14, color: Colors.black54, letterSpacing: 1)),
         ],
       ),
     );

lib/presentation/widgets/list/pokedex_list_header.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import '../../../l10n/app_localizations.dart';
 
 /// Barre de titre de la liste du Pokédex.
 class PokedexListHeader extends StatelessWidget {
@@ -9,13 +10,13 @@ class PokedexListHeader extends StatelessWidget {
     return Container(
       padding: const EdgeInsets.symmetric(horizontal: 16.0, vertical: 12.0),
       color: const Color(0xFF90A4AE),
-      child: const Row(
+      child: Row(
         mainAxisAlignment: MainAxisAlignment.spaceBetween,
         children: [
-          Icon(Icons.menu, color: Colors.black87),
-          Text('LIST - NATIONAL',
-              style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold, letterSpacing: 2)),
-          Icon(Icons.search, color: Colors.black87),
+          const Icon(Icons.menu, color: Colors.black87),
+          Text(AppLocalizations.of(context)!.listNational,
+              style: const TextStyle(fontSize: 24, fontWeight: FontWeight.bold, letterSpacing: 2)),
+          const Icon(Icons.search, color: Colors.black87),
         ],
       ),
     );