fix(registry): promote digest extraction (--raw | sha256sum)
Production hotfix. promote:image on main captured the full inspect output instead of the digest (--format '{{.Manifest.Digest}}' doesn't work on the tplInputs type), so imagetools create ...@<garbage> failed → :main/:latest never created. Fix: compute the digest from the raw manifest (--raw | sha256sum), verified to match the inspect Digest field.