maxfort.fi: DKIM record missing

Imported from GitHub issue El-SaMa/oma#167 by @El-SaMa.

DNS health engine (dns_health, oma.read_dns_health) flags maxfort.fi: DKIM missing. Zone is hosted by us, so the staff bell will keep firing.

Fix via staff tools only: read the DKIM key from Enhance/Glama, then oma.admin_dns_zone_read → oma.admin_dns_record → oma.confirm_tool, verify with oma.dns_lookup and re-run the DNS health check. Do not touch MX/SPF/mail.* beyond adding DKIM. Show the diff to the operator before confirming.