DR-018 — OKF producer trigger: chained off a successful walk, not scheduled, not operator-only

A successful ingest walk that changed source_documents chains a producer run ({132.16}); the concepts layer is the map over the records, so record deltas — not a calendar — drive concept regeneration (incremental via declare_file memoisation). Manual operator invocation is retained; publication gating (BI-20/21 + the review bridge) is unaffected. Owner-ratified on the S436 board.