docs(fix[nav]): Add glossary to Reference toctree

why: glossary.md was orphaned — not in any toctree, so users could not
discover it via sidebar navigation. {term} cross-references worked but
the page was invisible to browsing.
what:
- Add glossary to the Reference toctree in index.md

Author: tony

docs/index.md

@@ -110,6 +110,7 @@ topics/index
 
 reference/api/index
 reference/compatibility
+glossary
 ```
 
 ```{toctree}