dev: Update changelog for root CA validation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: vlasebian

CHANGELOG.md

@@ -12,6 +12,7 @@ For details about compatibility between different releases, see the **Commitment
 ### Added
 
 - Add tracing for LBS LNS and TTIGW protocol handlers.
+- Validate that root CA certificates are actually CA certificates on startup of The Things Stack, rejecting leaf certificates configured as root CAs.
 
 ### Changed