The eval steps listed hosts by hand and still referenced lyrathorpe-x1c,
which was removed (replaced by t400/macpro31), so CI errored. Derive the
NixOS and Darwin host lists from attrNames of nixos/darwinConfigurations
instead, so adding or removing a host needs no workflow change.
Verified locally under bash: all current hosts (edaas, macpro31, mbp,
t400, mac) evaluate; no removed host is referenced.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>