The form populated its candidate list via the admin-only
`GET /v2/users`, so opening Route Access Settings as a non-admin
caller (e.g. an org owner managing their own route in the
enterprise plugin) returned 403. Add a `queryUserDirectory` client
wrapper around the slim `/v2/user-directory` endpoint (gated to
platform admin OR org owner) and switch `getUserList` over. Response
shape is the same so the rest of the form is unchanged.
