fix(persistence): correctifs post-QA sur les repositories (ticket #13)

Corrige les ports, use cases, entités et l'implémentation Drift des
repositories suite aux retours de QA. flutter analyze propre, 24/24
tests verts, build APK debug validé.

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

lib/infrastructure/local/drift_repositories.dart

@@ -398,6 +398,14 @@ final class DriftActiveSessionRepository implements ActiveSessionRepository {
         .insertOnConflictUpdate(_activeRestStateCompanion(restState));
   }
 
+  @override
+  Future<domain.ActiveRestState?> findRestStateById(String id) async {
+    final row = await (database.select(
+      database.activeRestStates,
+    )..where((table) => table.id.equals(id))).getSingleOrNull();
+    return row == null ? null : _activeRestStateFromRow(row);
+  }
+
   @override
   Future<List<domain.ActiveSetResult>> listSetResults(String sessionId) async {
     final rows =