chore: re-version v1.21.0.0 -> v1.16.0.0 (lowest unclaimed slot)

The previous bump landed at v1.21.0.0 because gstack-next-version
advances past the highest claimed slot (v1.20.0.0 from #1252) rather
than picking the lowest unclaimed. v1.16-v1.18 are unclaimed and
v1.16.0.0 preserves monotonic version ordering on main once #1234
(v1.17), #1233 (v1.19), and #1252 (v1.20) merge after us.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -1,6 +1,6 @@
 # Changelog
 
-## [1.21.0.0] - 2026-04-28
+## [1.16.0.0] - 2026-04-28
 
 ## **Paired-agent tunnel allowlist now matches what the docs already promised. Catch-22 resolved, gate is unit-testable.**
 

VERSION

@@ -1 +1 @@
-1.21.0.0
+1.16.0.0

package.json

@@ -1,6 +1,6 @@
 {
   "name": "gstack",
-  "version": "1.21.0.0",
+  "version": "1.16.0.0",
   "description": "Garry's Stack — Claude Code skills + fast headless browser. One repo, one install, entire AI engineering workflow.",
   "license": "MIT",
   "type": "module",