All three workflow download sites (add --from, catalog install, step
install) passed no redirect_validator to open_url, so an HTTPS URL
redirecting to cleartext HTTP issued the insecure request before the
post-hoc geturl() check reported it. Shared validator now rejects
non-HTTPS redirects (loopback HTTP allowed) pre-follow, matching the
preset download path.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>