docs: add internal release changelog entry

Author: msukkari

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- Added a manually triggered cloud image release workflow for isolated internal deployments. [#1566](https://github.com/sourcebot-dev/sourcebot/pull/1566)
+
 ## [5.1.6] - 2026-08-10
 
 ### Added