The work/mirror clones were HTTPS end to end, so pushes went through git's
credential-helper config — which breaks the moment a stale absolute gh path
is baked into it (as gh auth setup-git once did with /usr/bin/gh). Reads stay
anonymous HTTPS; pushes now use an SSH push URL (derived from the clone URL,
overridable with OMARCHY_UPSTREAM_PUSH_URL), set idempotently on every run so
existing cached clones self-repair.