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

frontend/lib/data/repositories/local_onboarding_repository.dart

@@ -0,0 +1,18 @@
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:anyway/domain/repositories/onboarding_repository.dart';
+
+class LocalOnboardingRepository implements OnboardingRepository {
+  static const _key = 'onboardingCompleted';
+
+  @override
+  Future<bool> isOnboarded() async {
+    final prefs = await SharedPreferences.getInstance();
+    return prefs.getBool(_key) ?? false;
+  }
+
+  @override
+  Future<void> setOnboarded(bool value) async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setBool(_key, value);
+  }
+}