LAB: nightly affected_set case table + readers scan (PMAT-5802 follow-up) #5958

LAB follow-up to PMAT-5802 (flow-010 E5). scripts/affected_set.sh landed as a helper with no blocking check. Its two check scripts (check_affected_set.sh case table, check_affected_readers.sh readers scan) were pulled out of the PR path under C324 rule 7 (no operator yes, no 3 green nights, no gate retired).

Work: run both nightly as LAB on an idle machine, off the PR/merge-queue/release path; red opens/updates this ticket and stays silent; unmeasured or red 7 days stops them. Source of the scripts: PR #5954 commit 177852f (also kept in the cop inbox handoff). Owner: aprender-a3 until the cop reassigns.