docs: Phase 14 — Last reviewed line sweep across docs/

Per Phase 1 audit at cowork/docs-overhaul-phase-1-audit-2026-05-04/.
Adds a `> Last reviewed: 2026-05-05` line right after the H1 heading
of every doc that didn't already have one (41 files).

This dates the freshness clock for the future Phase 4 per-doc review.
The discipline going forward: when a doc's content gets a meaningful
edit, bump the date. When the date gets old (e.g., >6 months), the
doc earns a freshness-review pass.

Mechanical insertion via awk one-liner, applied to every docs/*.md
that didn't already match `grep -q 'Last reviewed:'`. Files that
already carried the line from earlier Phase 2 work (the navigation
index, the new connector docs, the new SCEP server / legacy-clients-
TLS-1.2 / release-verification docs, and the 5 per-connector deep
dives) were skipped to avoid duplicate insertion.

Net: every doc in docs/ now has a Last reviewed line.

docs/operator/approval-workflow.md

@@ -1,5 +1,7 @@
 # Issuance approval workflow
 
+> Last reviewed: 2026-05-05
+
 certctl can gate certificate issuance + renewal on a per-profile, two-person-integrity check. Compliance customers (PCI-DSS Level 1, FedRAMP Moderate / High, SOC 2 Type II, HIPAA) configure this on production-tier `CertificateProfile` rows so every renewal-loop tick or manual `POST /api/v1/certificates/{id}/renew` blocks at `JobStatusAwaitingApproval` until a different actor approves.
 
 Closes the procurement-checklist question "How do you enforce two-person integrity on cert issuance?" — without this surface the answer is "we don't"; with `requires_approval=true` on the profile, the answer is "here's the RBAC contract + here's the audit query that proves bypass mode is off in production."