feat(ui): écran Composition de séance-modèle

Ajoute l'écran de composition de séance-modèle
(presentation/workout_template_screen.dart), avec les ajustements
application/domaine/repositories nécessaires et la navigation depuis
l'accueil. flutter analyze propre, 12/12 tests verts, build APK debug
validé.

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

lib/application/app_bootstrap.dart

@@ -7,12 +7,14 @@ final class AppBootstrap {
     required this.exerciseUseCases,
     required this.mediaUseCases,
     required this.programUseCases,
+    required this.workoutTemplateUseCases,
   });
 
   final AppDatabase database;
   final ExerciseUseCases exerciseUseCases;
   final MediaUseCases mediaUseCases;
   final ProgramUseCases programUseCases;
+  final WorkoutTemplateUseCases workoutTemplateUseCases;
 
   static Future<AppBootstrap> create() async {
     final database = AppDatabase.open();
@@ -20,6 +22,7 @@ final class AppBootstrap {
     final exerciseRepository = DriftExerciseRepository(database);
     final mediaRepository = DriftMediaAssetRepository(database);
     final programRepository = DriftProgramRepository(database);
+    final templateRepository = DriftWorkoutTemplateRepository(database);
     final ids = LocalIdGenerator();
     const clock = SystemClock();
     const originDeviceId = 'local-device';
@@ -47,6 +50,13 @@ final class AppBootstrap {
         ids: ids,
         originDeviceId: originDeviceId,
       ),
+      workoutTemplateUseCases: WorkoutTemplateUseCases(
+        templateRepository: templateRepository,
+        programRepository: programRepository,
+        clock: clock,
+        ids: ids,
+        originDeviceId: originDeviceId,
+      ),
     );
   }