Returns the csrf token and ensures the csrftoken cookie is set.

Uses get_token() which triggers Django's CsrfViewMiddleware to set the cookie via process_response(). This avoids dual-cookie issues from manually calling response.set_cookie() alongside the middleware.

GET /csrf/?format=api
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "csrfToken": "CGTU02CiWVgTk8gW4UF6DLyxHEm7yXlCQKrGTJAdvLx2f5d5RsDnMU7uK2VDBIs7"
}