feat(exécution): dernière performance et meilleur score par exercice (ticket #81)

Ajoute la migration Drift v17 (colonne sourceExerciseIdSnapshot sur
workout_history_set_results et workout_history_step_results, index
associés), le port ExercisePerformanceReferenceRepository et son
implémentation Drift, et le use case
ExercisePerformanceReferenceUseCase (dernière performance + meilleur
score par métrique active pour un exercice donné).

Validé GO par Main : dart analyze propre (1 lint mineur de style),
178 tests (4 échecs préexistants sans rapport avec ce lot).

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

test/presentation/home_screen_test.dart

@@ -211,6 +211,9 @@ final class _FakeBootstrap implements AppDependencies {
       workoutHistoryUseCases = WorkoutHistoryUseCases(
         repository: _FakeWorkoutHistoryRepository(),
         clock: _FakeClock(DateTime.utc(2026, 7, 17, 12)),
+      ),
+      exercisePerformanceReferenceUseCase = ExercisePerformanceReferenceUseCase(
+        repository: _FakeExercisePerformanceReferenceRepository(),
       );
 
   @override
@@ -245,6 +248,9 @@ final class _FakeBootstrap implements AppDependencies {
 
   @override
   final WorkoutHistoryUseCases workoutHistoryUseCases;
+
+  @override
+  final ExercisePerformanceReferenceUseCase exercisePerformanceReferenceUseCase;
 }
 
 String _sessionSnapshot() {
@@ -704,3 +710,29 @@ final class _FakeWorkoutHistoryRepository implements WorkoutHistoryRepository {
   @override
   Future<void> saveStepResult(WorkoutHistoryStepResult result) async {}
 }
+
+final class _FakeExercisePerformanceReferenceRepository
+    implements ExercisePerformanceReferenceRepository {
+  @override
+  Future<bool> hasAnyCompletedHistoryForExercise(String exerciseId) async {
+    return false;
+  }
+
+  @override
+  Future<WorkoutHistorySetPerformance?> findLatestSetPerformance({
+    required String exerciseId,
+    required ActivePerformanceMeasures activeMeasures,
+    required int currentSetIndex,
+  }) async {
+    return null;
+  }
+
+  @override
+  Future<WorkoutHistoryMetricPerformance?> findBestMetricPerformance({
+    required String exerciseId,
+    required PerformanceMetric metric,
+    required ScoreInputMode scoreInputMode,
+  }) async {
+    return null;
+  }
+}