fix: address Copilot review round 4

- Reword the CI guarantee in AGENTS.md, docs/quality-gate.md and the
  pre-push-gate skill: a green gate means every check CI applies has
  passed here — the strongest predictor of green CI, not a proof — and
  name the residual (a test that passes only when slowed) as #1596's
  class to fix rather than headroom to keep.
- docs/quality-gate.md: cli's validate DID build, through `test`'s
  `pretest` hook; say that the build goes with the dropped `test` leg and
  `coverage:cli` builds once, later — in both places.
- Update the two source comments that still described `local:gate` as
  running `validate` (verify-skills.mjs, verify-build-gate.mjs).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PsmUAZ6aLUAFqenjJKSSRp
Signed-off-by: cliffhall <cliff@futurescale.com>

scripts/verify-skills.mjs

@@ -330,7 +330,7 @@ function main(argv = process.argv.slice(2)) {
   // The authoritative parse, when it is available — strictly a bonus, and only
   // from the EXACT pinned CLI.
   //
-  // `local:gate` runs `validate` (and therefore this) before the pinned
+  // `local:gate` runs `local:validate` (and therefore this) before the pinned
   // `verify:skills:cli` step, so a local CLI on any other version could reject
   // skills that CI's pinned validator accepts — and the gate would exit here,
   // never reaching the reproducible step (Copilot). Accepting merely "new enough"