Fix unreleased changelog version: b12 -> b11

Next release after 1.0.0b10 is b11, not b12.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jensens

CHANGES.md

@@ -1,6 +1,6 @@
 # Changelog
 
-## 1.0.0b12 (unreleased)
+## 1.0.0b11 (unreleased)
 
 ### Fixed