05 Exact Signoff v3 Audit

Verdict EXACT_SIGNOFF_FAIL. Arbitrary nonblank plan_id, any version>=1, and arbitrary nonblank reviewer name pass when fingerprint matches. Hardcoded reviewer allowlist conflicts with table CHECK. Signoff v3 is disconnected: tier signals and writer call old signoff, current plan is v2. No SAFE signoff exists now, but v3 is not authoritative and is self-invalidating through fingerprint inclusion.