Turns "point myblog.com at this site" into one action that consumes the URL-swap
tool. New DNSProviderService.find_zone_for_domain (longest zone-suffix match
across connected providers) + ensure_a_record upsert the A record via Cloudflare/
Route53, or return the exact record to add when nothing manages the zone.
WordPressService.attach_custom_domain orchestrates it: auto-create DNS (server IP
from SiteDomainService), optionally obtain a Let's Encrypt cert (the host vhost is
written first so certbot --nginx can validate), then migrate the site URL to the
domain via change_site_url. External steps degrade to warnings; only a requested
migration that errors aborts.
POST /wordpress/sites/<id>/domain (admin). Frontend: "Add Domain" button +
AttachDomainModal — enter a domain, optional HTTPS, and the result shows the
auto-created record or the exact A record to add manually.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
