docs: add cross-repo documentation links to docs site (#420)

Include the other-languages.md fragment from mq-rest-admin-common to show links to all language implementations on the docs home page.

Co-authored-by: wphillipmoore-claude <255925739+wphillipmoore-claude@users.noreply.github.com>

Author: wphillipmoore

docs/site/docs/index.md

@@ -37,3 +37,5 @@ shapes are stable but may evolve.
 ## License
 
 GNU General Public License v3.0
+
+--8<-- "other-languages.md"