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/detail/pokemon_stats_panel.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import '../../../domain/entities/pokemon.dart';
+import '../../../l10n/app_localizations.dart';
 
 /// Écran inférieur du détail : stats de base, description et éléments décoratifs.
 class PokemonStatsPanel extends StatelessWidget {
@@ -8,6 +9,7 @@ class PokemonStatsPanel extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final l = AppLocalizations.of(context)!;
     return Container(
       margin: const EdgeInsets.symmetric(horizontal: 16),
       padding: const EdgeInsets.all(8),
@@ -21,7 +23,7 @@ class PokemonStatsPanel extends StatelessWidget {
             Row(
               mainAxisAlignment: MainAxisAlignment.spaceBetween,
               children: [
-                const Text("BASE STATS", style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold, letterSpacing: 2)),
+                Text(l.baseStats, style: const TextStyle(fontSize: 24, fontWeight: FontWeight.bold, letterSpacing: 2)),
                 Text("MODEL: DS-01", style: TextStyle(fontSize: 12, color: Colors.grey[700], fontWeight: FontWeight.bold)),
               ],
             ),
@@ -38,7 +40,7 @@ class PokemonStatsPanel extends StatelessWidget {
               child: Text(
                 pokemon.description != null && pokemon.description!.isNotEmpty
                     ? '"${pokemon.description!}"'
-                    : '"No description available for this Pokémon."',
+                    : '"${l.noDescription}"',
                 style: const TextStyle(fontSize: 16, height: 1.5),
               ),
             ),