docs: link the archive branch (tag push not available; branch ref created instead)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162o68e5w3bpUBEVRQboUGG

Author: claude

README.md

@@ -54,7 +54,8 @@ As part of clarifying the ObjectStack / ObjectOS split:
   official Docker image and ObjectOS Cloud trials.
 - **Everything already released stays licensed as released**: historical
   source remains available under Apache-2.0 in this repository's git history
-  (archive tag: `archive/apache-final`). Nothing is retroactively withdrawn.
+  (archive branch: [`archive/apache-final`](https://github.com/objectstack-ai/objectos/tree/archive/apache-final)).
+  Nothing is retroactively withdrawn.
 
 ## Working on the docs