Add changelog section for v4.0.0-alpha.0

Author: immrsd

CHANGELOG.md

@@ -7,7 +7,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## Unreleased
+## 4.0.0-alpha.0 (2026-01-31)
 
 ### Added