Read External Source Scaffold release-execution-preflight preview metadata

Owner/admin metadata for the External Source Scaffold release-execution-preflight preview route. Returns accepted input shapes, supported workstreams, accepted owner release decisions, release execution preflight requirements, and a forced-false execution/release/smoke/write authority boundary. It performs no DB writes, release execution start, release decision execution, release executor dispatch, PR merge, owner release approval by helper, implementation execution, production release, production smoke execution, docs/public discovery mutation, route 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.