The clippy check's comment described `-D warnings -A clippy::pedantic` — the
`-A` half dropping pedantic from the CI gate — but the args were only
`-D warnings`, so pedantic was hard-denied contrary to the doc. Operator
call: pedantic should be gated. Encode that as the single source of truth:
set the workspace lint `pedantic = deny` (errors locally and in CI), and
rewrite the checks.nix comment to match. Args unchanged; `-D warnings` still
gates rustc + non-pedantic clippy warnings. No new failures — the tree was
already pedantic-clean under CI's `-D warnings`, which denied pedantic.
