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/sos_service_test.dart

@@ -0,0 +1,37 @@
+import 'dart:convert';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:http/http.dart' as http;
+import 'package:http/testing.dart';
+import 'package:travel_mate/services/sos_service.dart';
+
+void main() {
+  test('sendSos returns true on 200', () async {
+    final mockClient = MockClient((request) async {
+      expect(request.url.toString(), 'https://api.example.com/sos');
+      final body = json.decode(request.body) as Map<String, dynamic>;
+      expect(body['tripId'], 't1');
+      return http.Response('{}', 200);
+    });
+
+    final service = SosService(
+      baseUrl: 'https://api.example.com',
+      client: mockClient,
+    );
+
+    final result = await service.sendSos(tripId: 't1', lat: 1, lng: 2);
+    expect(result, isTrue);
+  });
+
+  test('sendSos returns false on error', () async {
+    final mockClient = MockClient((request) async {
+      return http.Response('fail', 500);
+    });
+    final service = SosService(
+      baseUrl: 'https://api.example.com',
+      client: mockClient,
+    );
+
+    final result = await service.sendSos(tripId: 't1', lat: 0, lng: 0);
+    expect(result, isFalse);
+  });
+}