chore: add changelog entry for review agent ack reaction

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Gavin Williams

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- [Experimental] Review agent now acknowledges receipt of the `review` command by adding a reaction to the triggering comment. The reaction is configurable via `REVIEW_AGENT_ACK_REACTION` (default: `eyes`). [#1174](https://github.com/sourcebot-dev/sourcebot/pull/1174)
+
 ## [4.17.1] - 2026-05-04
 
 ### Added