Add OAuth changelog entry under Unreleased

Author: MajidAbuRmila

CHANGELOG.md

@@ -6,13 +6,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/) and this
 
 ## [Unreleased]
 
-### Added
-
 ### Changed
 
-### Fixed
-
-### Removed
+- MCP authentication moved to OAuth 2.1 — no `CPLN_TOKEN` env var required for the hosted MCP server. On first use, your AI client prompts you to sign in and pick which Control Plane organizations it may operate on.
 
 ## [1.3.2] - 2026-05-13