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/application.dart

@@ -3,3 +3,6 @@
 /// This layer owns use cases and ports. It may depend on domain, but concrete
 /// adapters are wired only from the composition root.
 library;
+
+export 'ports.dart';
+export 'use_cases.dart';