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/infrastructure/local/local_id.dart

@@ -1,12 +1,17 @@
 import 'dart:math';
 
+import '../../application/ports.dart';
+
 const _crockfordBase32 = '0123456789ABCDEFGHJKMNPQRSTVWXYZ';
 
-final class LocalIdGenerator {
+final class LocalIdGenerator implements IdGenerator {
   LocalIdGenerator({Random? random}) : _random = random ?? Random.secure();
 
   final Random _random;
 
+  @override
+  String newId() => newUlid();
+
   String newUlid({DateTime? now}) {
     final timestamp = (now ?? DateTime.now().toUtc()).millisecondsSinceEpoch;
     final buffer = StringBuffer();