Keyless, by digest, with a verification pass against the calling workflow's
own identity right after signing. Signatures use the .sig tag layout rather
than the OCI-referrer bundle cosign 3 writes by default, since that is what
the verifiers people run today read. Dependabot is pointed at the action so
the cosign-installer pin keeps moving.
Claude-Session: https://claude.ai/code/session_01A5zMqzaUg1Snur4Yg8xJGa