Implement the step definitions for EenZaakOpenen.feature against the
existing AclService, with an in-memory gateway standing in for the OpenZaak
Zaken API. The scenario now passes: a domain registration is default-filled
into a ZaakRequest (ADR-0003) and the created zaak URL is returned.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
