NS hostnames stored in happyDomain's abstract.Origin service are encoded
relative to the zone apex (e.g. "ns0" instead of "ns0.example.com.").
normalizeNSList was calling dns.Fqdn() directly, turning "ns0" into the
useless single-label "ns0." rather than the correct FQDN.
Expose domain_name in ServiceOpts so happyDomain auto-fills the zone
apex at service scope, then use sdk.JoinRelative in normalizeNSList to
absolutize relative labels. Absolute FQDNs (trailing dot) are kept
as-is so external nameservers round-trip safely.
