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/domain/domain.dart

@@ -2,3 +2,5 @@
 ///
 /// Keep this layer free from Flutter, Drift, platform APIs, and IO.
 library;
+
+export 'entities.dart';