docker push was hanging: "Client.Timeout exceeded while awaiting
headers" doing a TLS handshake against harbor-core.harbor.svc.cluster.local,
which only ever speaks plain HTTP (TLS disabled cluster-wide by
design). Docker defaults to HTTPS for any bare registry hostname
regardless of network path — that default has nothing to do with
whether traffic routes through Contour/Ingress, contrary to what an
earlier pending-items note assumed. Adds --insecure-registry to the
dind container's dockerd startup args.