control runs blackbox_exporter on loopback, probing each nameserver's
public v4+v6 address for every zone: SOA (zone served) and DNSKEY (still
signed, since blackbox has no DO-bit option). Probe definitions are
shared between the exporter config and the VictoriaMetrics scrape jobs
so they can't drift. Verified live against ns1/ns2 over v4 and v6.
Berwn