(plan) convert original implement plan to mock api

tasks/5.16-audit-ci-gate.md

@@ -1,6 +1,8 @@
-# 5.16 — pnpm audit + govulncheck CI gate (GREEN)
+# 5.16 — pnpm audit CI gate (GREEN)
 
 Phase: 5 — Chat + Rate Limiter (Surface D)
 Stage: GREEN
 
-- [ ] `pnpm audit` + `govulncheck` in CI, fail build on high severity
+- [ ] `pnpm audit` in CI, fail build on high severity
+
+`govulncheck` dropped from this task — no Go code in this repo.