ci: parity_receipt_denominator.sh verify mode is never run — only --self-test is wired (#3577 guard is dark)

[noahgift]

Found by the S1 post-hoc quorum of #3669 (sonnet lane, verified by apr-features).

scripts/parity_receipt_denominator.sh has three modes: verify (no args), --print, and --self-test. On main, CI runs only --self-test (.github/workflows/ci.yml:1234 and :1258). The verify mode is not run by any workflow, Makefile target, or script (git grep on origin/main). Verify mode is the one that recomputes the receipt count from the tree and compares it with evidence/parity/EXPECTED_RECEIPTS.

So the defect #3577 exists to catch goes unchecked. A receipt added or removed without bumping EXPECTED_RECEIPTS passes CI, because the self-test only runs synthetic fixtures.

Today the verify mode passes on a git archive origin/main snapshot: 7 receipts, and EXPECTED_RECEIPTS says 7. Nothing is broken right now; the guard just never runs.

Fix: add a bash scripts/parity_receipt_denominator.sh (verify) line next to the --self-test line. This is a workflow edit, so it needs a cop check-in and a 3/3 quorum. Also plant a mutation (EXPECTED_RECEIPTS 7 -> 8) to prove the job goes red.

[noahgift]

Fix on branch GH-4425-parity-denominator-verify-wired @7653b2972: scripts/check_parity_receipt_denominator.sh runs verify mode. As a check_*.sh it is picked up by guard_tree.sh (self-test row + run row) in the existing --no-cargo step, so no workflow edit is needed. Mutation: EXPECTED_RECEIPTS 7→8 exits 1 ("says 8; the tree holds 7"); a wrapper that swallows the exit or runs the wrong mode fails its self-test. Quorum (degraded: same-family): sonnet APPROVE, haiku APPROVE. Queued for fold by aprender-59.