PostgreSQL blocking family: an operator now learns who headed a blocking chain, in what state, and how long the sessions behind it had really waited — PG_BLOCKING_CHAIN from the sampled edges, PG_LOCK_WAIT_EVENTS from the engine's own log lines, PG_LONG_RUNNING_QUERY from the active sessions, and a blocked-sessions anomaly whose baseline counts a quiet capture as zero (partial #3691, lane 17) - #3750