Delete an active domain (soft-delete, reversible via revoke)

Mark an active domain as deleted. The domain's <code>status</code> is moved from <code>"active"</code> to <code>"deleted"</code> and its mailboxes are taken out of sending rotation.

<strong>Preconditions:</strong> The domain must currently be in <code>status: "active"</code>. Calling delete on a domain that is <code>inProgress</code>, already <code>deleted</code>, <code>failed</code>, or <code>expired</code> is rejected.

<strong>AnnualFlexi behaviour:</strong> When the parent order is on the <code>annualFlexi</code> plan, deleting the domain reserves a slot tied to the order so a replacement domain can be swapped in later for the remaining term. Other plan types do not create a reserved slot.

<strong>Reversible:</strong> A deleted domain can be restored via <code>POST /v1/domain/{id}/revoke</code> as long as it is still in <code>status: "deleted"</code>. Final hard-removal from the registrar is performed asynchronously by an internal cron after deletion.

This endpoint operates on a single domain <code>id</code> at a time — use the domain's <code>id</code> from <code>GET /v1/domain</code>, not the <code>orderId</code>.