Unified CI on nixos repo is proven end-to-end (CI run on 836f80a deployed to
muffin successfully and yarn's pull URL now serves from the new build). The
two per-repo git-crypt keys are no longer in use by any active pipeline.
Old dotfiles and server-config repos had Gitea Actions disabled before this
commit, so no CI race possible.
The two legacy entries git-crypt-key-{dotfiles,server-config} stay until
muffin has deployed this config at least once and the new CI pipeline is
green. Phase 6 removes them after cutover.
