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/home_screen.dart

@@ -5,13 +5,21 @@ import '../domain/domain.dart';
 import 'exercise_library_screen.dart';
 import 'history_screen.dart';
 import 'program_screen.dart';
+import 'theme.dart';
 import 'workout_execution_screen.dart';
 import 'workout_template_screen.dart';
 
 final class HomeScreen extends StatefulWidget {
-  const HomeScreen({required this.bootstrap, super.key});
+  const HomeScreen({
+    required this.bootstrap,
+    this.themeMode = ThemeMode.system,
+    this.onThemeModeChanged,
+    super.key,
+  });
 
   final AppBootstrap bootstrap;
+  final ThemeMode themeMode;
+  final ValueChanged<ThemeMode>? onThemeModeChanged;
 
   @override
   State<HomeScreen> createState() => _HomeScreenState();
@@ -29,7 +37,22 @@ final class _HomeScreenState extends State<HomeScreen> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('GameTime')),
+      appBar: AppBar(
+        title: const GameTimeLogo(),
+        actions: [
+          PopupMenuButton<ThemeMode>(
+            tooltip: 'Thème',
+            initialValue: widget.themeMode,
+            icon: const Icon(Icons.contrast),
+            onSelected: widget.onThemeModeChanged,
+            itemBuilder: (context) => const [
+              PopupMenuItem(value: ThemeMode.system, child: Text('Système')),
+              PopupMenuItem(value: ThemeMode.light, child: Text('Clair')),
+              PopupMenuItem(value: ThemeMode.dark, child: Text('Sombre')),
+            ],
+          ),
+        ],
+      ),
       body: ListView(
         children: [
           FutureBuilder<ActiveWorkoutSession?>(
@@ -46,17 +69,20 @@ final class _HomeScreenState extends State<HomeScreen> {
                 setIndex: session.currentSetIndex,
               );
               final exercise = plan.exerciseAt(position);
-              return MaterialBanner(
-                content: Text(
-                  'Séance en cours — Reprendre · ${exercise.name}, '
-                  'série ${position.setIndex + 1}/${exercise.setsCount}',
-                ),
-                actions: [
-                  TextButton(
-                    onPressed: () => _resume(session),
-                    child: const Text('Reprendre'),
+              return CourtBlazerAccentPanel(
+                margin: const EdgeInsets.all(12),
+                child: MaterialBanner(
+                  content: Text(
+                    'Séance en cours — Reprendre · ${exercise.name}, '
+                    'série ${position.setIndex + 1}/${exercise.setsCount}',
                   ),
-                ],
+                  actions: [
+                    TextButton(
+                      onPressed: () => _resume(session),
+                      child: const Text('Reprendre'),
+                    ),
+                  ],
+                ),
               );
             },
           ),