Create or overwrite a custom DNS record (upsert)

Create a TXT, CNAME, A, or AAAA record on the domain's DNS zone. The request is validated against Winnr-managed records — attempts to create records that collide with MX, inbound A, DKIM, or SPF return 409 managed_record_collision. Upsert semantics: if a tracked custom record already exists at the same (name, type), it is overwritten in place (same record id, new value/ttl) and the response sets overwrote_existing: true. If the zone holds an untracked record at the same (name, type) (e.g. a tracking CNAME created at provision time), it is adopted: overwritten in place and added to the domain's custom records. To change DMARC, use PUT /v1/domains/{id}/dmarc.