feat: Add services for managing trip-related data

- Implement EmergencyService for handling emergency contacts per trip.
- Create GuestFlagService to manage guest mode flags for trips.
- Introduce NotificationService with local notification capabilities.
- Add OfflineFlagService for managing offline caching flags.
- Develop PackingService for shared packing lists per trip.
- Implement ReminderService for managing reminders/to-dos per trip.
- Create SosService for dispatching SOS events to a backend.
- Add StorageService with album image upload functionality.
- Implement TransportService for managing transport segments per trip.
- Create TripChecklistService for storing and retrieving trip checklists.
- Add TripDocumentService for persisting trip documents metadata.

test: Add unit tests for new services

- Implement tests for AlbumService, BudgetService, EmergencyService, GuestFlagService, PackingService, ReminderService, SosService, TransportService, TripChecklistService, and TripDocumentService.
- Ensure tests cover adding, loading, deleting, and handling corrupted payloads for each service.

test/services/trip_checklist_service_test.dart

@@ -0,0 +1,63 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:travel_mate/models/checklist_item.dart';
+import 'package:travel_mate/services/trip_checklist_service.dart';
+
+void main() {
+  late TripChecklistService service;
+  const tripId = 'trip-123';
+
+  setUp(() {
+    SharedPreferences.setMockInitialValues({});
+    service = TripChecklistService();
+  });
+
+  test('adds and loads checklist items', () async {
+    final created = ChecklistItem.newItem(id: '1', label: 'Préparer passeport');
+    await service.addItem(tripId, created);
+
+    final result = await service.loadChecklist(tripId);
+
+    expect(result, hasLength(1));
+    expect(result.first.label, 'Préparer passeport');
+    expect(result.first.isDone, isFalse);
+  });
+
+  test('toggles completion state', () async {
+    final item = ChecklistItem.newItem(id: '1', label: 'Acheter billets');
+    await service.addItem(tripId, item);
+
+    final toggled = await service.toggleItem(tripId, '1');
+
+    expect(toggled.first.isDone, isTrue);
+
+    final toggledBack = await service.toggleItem(tripId, '1');
+    expect(toggledBack.first.isDone, isFalse);
+  });
+
+  test('deletes items and keeps list consistent', () async {
+    final itemA = ChecklistItem.newItem(id: '1', label: 'Adapter prise');
+    final itemB = ChecklistItem.newItem(id: '2', label: 'Chargeur');
+    await service.addItem(tripId, itemA);
+    await service.addItem(tripId, itemB);
+
+    final afterDelete = await service.deleteItem(tripId, '1');
+
+    expect(afterDelete, hasLength(1));
+    expect(afterDelete.first.id, '2');
+
+    final persisted = await service.loadChecklist(tripId);
+    expect(persisted, hasLength(1));
+    expect(persisted.first.id, '2');
+  });
+
+  test('handles corrupted payload gracefully', () async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString('checklist_$tripId', 'not-json');
+
+    final items = await service.loadChecklist(tripId);
+
+    expect(items, isEmpty);
+    expect(prefs.getString('checklist_$tripId'), isNull);
+  });
+}