docs: add PR link to desktop skill hub changelog entry

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: quickbeard

CHANGELOG.md

@@ -17,6 +17,7 @@ file is the human-readable summary of what changed and why.
   included, one real copy plus links for the other agents. Re-installing
   offers a safe overwrite, and everything rides the same shared sign-in as
   `codev skill` and `codevhub`.
+  ([#331](https://github.com/quickbeard/codev-code/pull/331))
 
 ### Language