Cancel a scheduled deletion

Undoes DELETE /organization/{id} inside its 30-day window: the purge is canceled and the organization becomes writable again. Connections do not come back, because their stored credentials were deleted at the original delete; each has to be re-authorized by hand. Requires org:manage, so an Org Admin can restore and not only the Owner who could delete. No body and no step-up. Refuses with 409 when the organization is not currently scheduled for deletion or the window has passed, with 403 organization_blocked when the organization is suspended, and with subscription_required when the plan lapsed (the delete canceled the Stripe subscription, so a restore needs a new one).