Update changelog

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Changed
+
+- Deprecated `firstBuyDate` in favor of `dateOfFirstActivity` in the endpoint `GET api/v1/portfolio/holding/:dataSource/:symbol`
+
 ## 2.231.0 - 2026-01-17
 
 ### Changed