feat(wip): Update entities and adopt a proper repository workflow for trip "obtention"

frontend/lib/domain/repositories/onboarding_repository.dart

@@ -0,0 +1,7 @@
+abstract class OnboardingRepository {
+  /// Returns true when the user accepted the onboarding agreement
+  Future<bool> isOnboarded();
+
+  /// Sets the onboarding completion flag
+  Future<void> setOnboarded(bool value);
+}