feat(plugin-audit): sys_activity gains writer-stamped read-rule columns with an idempotent backfill, and the withheld-row rule is a predicate with no SYSTEM pre-scan (ADR-0139 E6)

feat(plugin-audit): sys_activity gains writer-stamped read-rule columns with an idempotent backfill, and the withheld-row rule is a predicate with no SYSTEM pre-scan (ADR-0139 E6) #15307