ssh.git.trevon.dev no longer resolves (the experimental mirror run failed
with 'Could not resolve hostname'), and main already switched the mirror
remote to git.trevon.dev, where the mirror push succeeds. The policy test
still required the old host and forbade the new one, failing Tests on
every platform for main. Require git.trevon.dev, forbid the dead name,
and update the mirroring doc.
