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/transport_service_test.dart

@@ -0,0 +1,75 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:travel_mate/models/transport_segment.dart';
+import 'package:travel_mate/services/transport_service.dart';
+
+void main() {
+  const tripId = 'trip-transport-1';
+  late TransportService service;
+
+  setUp(() {
+    SharedPreferences.setMockInitialValues({});
+    service = TransportService();
+  });
+
+  test('adds and loads a segment', () async {
+    final seg = TransportSegment.newSegment(
+      id: 'seg1',
+      type: 'flight',
+      carrier: 'AF',
+      number: '763',
+      departureCode: 'CDG',
+      arrivalCode: 'JFK',
+      departureUtc: DateTime.utc(2026, 4, 10, 7, 0),
+      arrivalUtc: DateTime.utc(2026, 4, 10, 11, 0),
+      pnr: 'ABC123',
+    );
+
+    await service.addSegment(tripId, seg);
+    final loaded = await service.loadSegments(tripId);
+
+    expect(loaded, hasLength(1));
+    expect(loaded.first.number, '763');
+    expect(loaded.first.status, 'scheduled');
+  });
+
+  test('updates status', () async {
+    final seg = TransportSegment.newSegment(
+      id: 'seg1',
+      type: 'train',
+      carrier: 'TGV',
+      number: '8401',
+      departureCode: 'PAR',
+      arrivalCode: 'BRU',
+      departureUtc: DateTime.utc(2026, 5, 1, 8, 30),
+      arrivalUtc: DateTime.utc(2026, 5, 1, 10, 30),
+    );
+    await service.addSegment(tripId, seg);
+
+    final updated = await service.updateStatus(tripId, 'seg1', 'delayed');
+
+    expect(updated.first.status, 'delayed');
+  });
+
+  test('deletes segment and handles corrupted payload', () async {
+    final seg = TransportSegment.newSegment(
+      id: 'seg1',
+      type: 'bus',
+      carrier: 'FLX',
+      number: '12',
+      departureCode: 'AMS',
+      arrivalCode: 'BRU',
+      departureUtc: DateTime.utc(2026, 6, 1, 9, 0),
+      arrivalUtc: DateTime.utc(2026, 6, 1, 11, 30),
+    );
+    await service.addSegment(tripId, seg);
+    await service.deleteSegment(tripId, 'seg1');
+
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString('trip_transport_$tripId', 'bad-json');
+
+    final loaded = await service.loadSegments(tripId);
+    expect(loaded, isEmpty);
+    expect(prefs.getString('trip_transport_$tripId'), isNull);
+  });
+}