feat(exercice): résolution effective et auto-advance des chronos d'étapes (ticket #76)

Ajoute la résolution effective de l'auto-enchaînement (application/use_cases.dart)
et son support dans l'adapter Drift (infrastructure/local/drift_repositories.dart).
flutter pub get OK, dart format appliqué, analyze propre (mêmes infos
préexistantes), tests verts, build APK debug validé.

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

lib/infrastructure/local/drift_repositories.dart

@@ -3047,8 +3047,7 @@ domain.Exercise _exerciseFromPayload(RemoteSyncedItem item) {
     defaultTargetReps: payload['defaultTargetReps'] as int?,
     defaultTargetScore: (payload['defaultTargetScore'] as num?)?.toDouble(),
     defaultTargetScoreTimeMs: payload['defaultTargetScoreTimeMs'] as int?,
-    autoStartNextTimedStep:
-        payload['autoStartNextTimedStep'] as bool? ?? true,
+    autoStartNextTimedStep: payload['autoStartNextTimedStep'] as bool? ?? true,
     steps: _stepsFromPayload(payload['steps']),
     archivedAt: _dateTimeFromPayload(payload['archivedAt']),
   );