docs(index): fix toctree formatting, remove hide-toc

why: The hide-toc frontmatter was suppressing the sidebar ToC,
and the toctree directive was malformed (stray :hidden: outside block).

what:
- Remove hide-toc: true frontmatter
- Remove stray "## Table of Contents" and ":hidden:" text
- Add :hidden: to first toctree directive (matches libvcs pattern)

Author: tony

docs/index.md

@@ -1,7 +1,3 @@
----
-hide-toc: true
----
-
 (index)=
 
 # libtmux
@@ -10,12 +6,9 @@ hide-toc: true
 :start-after: </div>
 ```
 
-## Table of Contents
-
-:hidden:
-
 ```{toctree}
 :maxdepth: 2
+:hidden:
 
 quickstart
 about