feat(domains): support apex domains and non-.com TLDs

Loosen the custom-domain regex to accept apex domains (1+ labels) in
addition to subdomains; the TLD already allowed any letters. Suppress
the CNAME record for apex hostnames since a CNAME is invalid at the zone
apex, and surface only the A record there. Drop the frontend apex
rejection and the misleading ".com" input suffix, and render the
domain-input prefix/suffix addons only when set.

pnpm-lock.yaml

@@ -144,6 +144,9 @@ importers:
       nanoid:
         specifier: ^5.1.5
         version: 5.1.6
+      tldts:
+        specifier: ^6.1.86
+        version: 6.1.86
       zod:
         specifier: 4.2.1
         version: 4.2.1