Update header on CHANGELOG

Author: camdecoster

CHANGELOG.md

@@ -11,6 +11,9 @@ where X.Y.Z is the semver of most recent plotly.js release.
 
 ## [X.Y.Z] -- UNRELEASED
 
+
+## [v4.0.0] -- 2026-08-24
+
 ### Added
 - Add `minscale`, `maxscale` geo plot attributes [[#7371](https://github.com/plotly/plotly.js/pull/7371)], with thanks to @mojoaxel for the contribution!
 - Enable TypeScript compatibility within the library and start exporting types [[#7680](https://github.com/plotly/plotly.js/pull/7680)]