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/getting-started/advanced-demo.md

@@ -1,5 +1,7 @@
 # Advanced Demo: Certificate Lifecycle End-to-End
 
+> Last reviewed: 2026-05-05
+
 This demo goes beyond browsing pre-loaded data. You'll create a team, register an owner, set up an issuer, create a certificate, trigger renewal, and watch everything appear in the dashboard in real time. Each step includes a technical explanation of what's happening inside certctl and why the system is designed that way.
 
 **Time**: 15-20 minutes

docs/getting-started/concepts.md

@@ -1,5 +1,7 @@
 # Understanding Certificates: A Beginner's Guide
 
+> Last reviewed: 2026-05-05
+
 If you've never worked with TLS certificates before, this guide will get you up to speed. By the end, you'll understand what certificates are, why they matter, and why the industry's move toward shorter certificate lifespans — down to 47 days by 2029 — makes automated lifecycle management essential.
 
 ## Contents

docs/getting-started/examples.md

@@ -1,5 +1,7 @@
 # Deployment Examples
 
+> Last reviewed: 2026-05-05
+
 Five turnkey docker-compose scenarios, each runnable in under 5 minutes. Pick the one closest to your setup.
 
 ## Which Example Should I Use?

docs/getting-started/quickstart.md

@@ -1,5 +1,7 @@
 # Quick Start Guide
 
+> Last reviewed: 2026-05-05
+
 Certificate lifespans are dropping to **47 days by 2029**. At that cadence, a team managing 100 certificates is processing 7+ renewals per week — every week, forever. Manual processes break. certctl automates the entire lifecycle: issuance, renewal, deployment, revocation, and audit — with zero human intervention.
 
 This guide gets you running in 5 minutes and walks you through everything certctl does.

docs/getting-started/why-certctl.md

@@ -1,5 +1,7 @@
 # Why certctl?
 
+> Last reviewed: 2026-05-05
+
 Certificate management is broken at every scale between "one domain on Let's Encrypt" and "Fortune 500 budget for Venafi." certctl fills that gap: a self-hosted platform that automates the entire certificate lifecycle, works with any CA, deploys to any server, and keeps private keys on your infrastructure. It's free, source-available, and you own everything.
 
 ## The Math That Forces the Decision