Add API root endpoint at /api/

Created /api/ endpoint that returns JSON with:
- API status
- Available endpoints
- Version information

This fixes the "Not Found" error when accessing /api/ and
provides a useful API discovery endpoint for clients.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

config/urls.py

@@ -11,11 +11,15 @@ from users.urls import api_urlpatterns as users_api_urls, web_urlpatterns as use
 from tasks.urls import api_urlpatterns as tasks_api_urls, web_urlpatterns as tasks_web_urls
 from sync.urls import api_urlpatterns as sync_api_urls
 from notifications.urls import api_urlpatterns as notifications_api_urls
+from .views import api_root
 
 urlpatterns = [
     # Admin
     path('admin/', admin.site.urls),
 
+    # API root
+    path('api/', api_root, name='api-root'),
+
     # API endpoints
     path('api/users/', include(users_api_urls)),
     path('api/tasks/', include(tasks_api_urls)),