Claim a domain held by another account

Checks the claim TXT record and moves a never-verified domain from the account that holds it to the caller's team, with its verification reset and any mail the previous holder still had queued through it cancelled. POST /v1/domains answers 409 with code domain_claimable and the record when this applies. 422 claim_record_missing when the record is not visible, 503 dns_unavailable when the lookup itself failed. The previous holder is notified. Requires the domain:write scope; 20 checks per hour per team.