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/reminder_service_test.dart

@@ -0,0 +1,45 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:travel_mate/models/reminder_item.dart';
+import 'package:travel_mate/services/reminder_service.dart';
+
+void main() {
+  const tripId = 'trip-reminders-1';
+  late ReminderService service;
+
+  setUp(() {
+    SharedPreferences.setMockInitialValues({});
+    service = ReminderService();
+  });
+
+  test('adds and toggles reminders', () async {
+    final r = ReminderItem.newItem(
+      id: 'r1',
+      title: 'Check-in en ligne',
+      dueAt: DateTime.utc(2026, 4, 10, 7),
+    );
+    await service.addReminder(tripId, r);
+    var list = await service.loadReminders(tripId);
+    expect(list.single.isDone, isFalse);
+
+    list = await service.toggleReminder(tripId, 'r1');
+    expect(list.single.isDone, isTrue);
+  });
+
+  test('deletes and clears corrupted payload', () async {
+    final r = ReminderItem.newItem(
+      id: 'r1',
+      title: 'Acheter métro pass',
+      dueAt: DateTime.utc(2026, 4, 1),
+    );
+    await service.addReminder(tripId, r);
+    var list = await service.deleteReminder(tripId, 'r1');
+    expect(list, isEmpty);
+
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString('reminders_$tripId', 'oops');
+    list = await service.loadReminders(tripId);
+    expect(list, isEmpty);
+    expect(prefs.getString('reminders_$tripId'), isNull);
+  });
+}