feat(application): couche application avec use cases et repositories

Ajoute les entités du domaine (domain/entities.dart), les ports de
repository (application/ports.dart), les use cases (application/use_cases.dart)
et leur implémentation Drift (infrastructure/local/drift_repositories.dart).
flutter analyze propre, tests unitaires verts, build APK debug validé.

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

lib/application/ports.dart

@@ -0,0 +1,49 @@
+import '../domain/domain.dart';
+
+abstract interface class Clock {
+  DateTime now();
+}
+
+final class SystemClock implements Clock {
+  const SystemClock();
+
+  @override
+  DateTime now() => DateTime.now().toUtc();
+}
+
+abstract interface class IdGenerator {
+  String newId();
+}
+
+abstract interface class ExerciseRepository {
+  Future<Exercise?> findById(String id);
+  Future<List<Exercise>> listActive();
+  Future<void> save(Exercise exercise);
+}
+
+abstract interface class ProgramRepository {
+  Future<Program?> findById(String id);
+  Future<void> save(Program program);
+  Future<void> saveExercise(ProgramExercise exercise);
+}
+
+abstract interface class WorkoutTemplateRepository {
+  Future<WorkoutTemplate?> findById(String id);
+  Future<void> save(WorkoutTemplate template);
+  Future<void> saveProgram(WorkoutTemplateProgram program);
+  Future<void> saveOverride(WorkoutTemplateExerciseOverride override);
+}
+
+abstract interface class ActiveSessionRepository {
+  Future<ActiveWorkoutSession?> findById(String id);
+  Future<void> save(ActiveWorkoutSession session);
+  Future<void> saveSetResult(ActiveSetResult result);
+  Future<void> saveRestState(ActiveRestState restState);
+  Future<List<ActiveSetResult>> listSetResults(String sessionId);
+  Future<List<ActiveRestState>> listRestStates(String sessionId);
+}
+
+abstract interface class WorkoutHistoryRepository {
+  Future<void> save(WorkoutHistory history);
+  Future<void> saveSetResult(WorkoutHistorySetResult result);
+}