Read External Source Scaffold completion-audit preview metadata

Owner/admin metadata for the External Source Scaffold completion-audit preview route. Returns accepted input shapes, supported workstreams, expected artifact inventory, completion audit requirements, and a forced-false completion-audit/owner-closeout/program-completion/production-launch/write authority boundary. It performs no DB writes, completion audit write by helper, owner completion approval by helper, program completion by helper, production launch, scaffold artifact mutation, validation execution by helper, docs/API/OpenAPI mutation, ledger write by helper, archive publication by helper, release evidence recording by helper, release execution start, release decision execution, release executor dispatch, PR merge, owner release approval by helper, implementation execution, production release, production smoke execution, public discovery mutation, Seller OS mutation, trust/ranking mutation, x402/wallet/settlement mutation, provider dispatch, browser automation, memory write/promotion, live finance action, or private Full ECF exposure.