artifact-9642983578.zip provenance anchor

Chose the retained GitHub Actions artifact cases/review/oss-governance-adjudication-v1/artifact-9642983578.zip over trusting standalone JSON files or locally repeated hashes because it independently proves documents.json and v1.2-coding-package.json match workflow run 33063470968. The verifier never extracts it: it validates the full archive defensively, then reads only those two required members for byte-exact comparison.