feat(ui): identité visuelle Court Blazer sur toute l'app (ticket #17)

Ajoute le thème centralisé (presentation/theme.dart) basé sur les
polices Anton/Archivo et l'applique à tous les écrans (accueil,
bibliothèque d'exercices, programme, séance-modèle, exécution de
séance, historique). flutter analyze propre, 27/27 tests verts, build
APK debug validé.

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

lib/presentation/game_time_app.dart

@@ -2,21 +2,32 @@ import 'package:flutter/material.dart';
 
 import '../application/app_bootstrap.dart';
 import 'home_screen.dart';
+import 'theme.dart';
 
-final class GameTimeApp extends StatelessWidget {
+final class GameTimeApp extends StatefulWidget {
   const GameTimeApp({required this.bootstrap, super.key});
 
   final AppBootstrap bootstrap;
 
+  @override
+  State<GameTimeApp> createState() => _GameTimeAppState();
+}
+
+final class _GameTimeAppState extends State<GameTimeApp> {
+  var _themeMode = ThemeMode.system;
+
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
       title: 'GameTime',
-      theme: ThemeData(
-        colorScheme: ColorScheme.fromSeed(seedColor: const Color(0xFF0E7C66)),
-        useMaterial3: true,
+      theme: courtBlazerLightTheme(),
+      darkTheme: courtBlazerDarkTheme(),
+      themeMode: _themeMode,
+      home: HomeScreen(
+        bootstrap: widget.bootstrap,
+        themeMode: _themeMode,
+        onThemeModeChanged: (mode) => setState(() => _themeMode = mode),
       ),
-      home: HomeScreen(bootstrap: bootstrap),
     );
   }
 }