* feat(db): five pgx pools with fixed session settings and Prometheus tracing
* feat(guards): per-family observe/enforce guards with client slots, deadlines and a shadow budget
* fix(guards): attribute only guard deadlines and classify like the handlers
* feat(db): route API statements by sqlc name; class C always unnamed
* feat(admin): statement statistics by sqlc name; create pg_stat_statements where allowed
* fix(db): skip pg_stat_statements when no schema is creatable
* feat(background): index health against post-rebuild baselines, Postgres activity, job and ingest metrics
* feat: separate API, ingest and maintenance stores; guards on the public API; metrics listener
* fix(db): keep ingest writes waiting, size the ingest pool to the host, tidy
* test(db): give the statements probe a query id of its own
