Fix Django API routing and authentication issues

- Add django.contrib.auth to INSTALLED_APPS
- Fix URL routing structure for proper API endpoints
- Add API root endpoint with endpoint information
- Verify all API endpoints working correctly

backend/poker_api/settings.py

@@ -15,6 +15,7 @@ ALLOWED_HOSTS = ['localhost', '127.0.0.1']
 
 INSTALLED_APPS = [
     'django.contrib.contenttypes',
+    'django.contrib.auth',
     'django.contrib.staticfiles',
     'rest_framework',
     'corsheaders',