sphinx is not rendering enum members

This worked originally; at some point it changed.

https://github.com/sphinx-doc/sphinx/issues/1609

I tried just slotting this into our auto-generated tree, but it looks like this will only work once we re-structure the docs to be better organized and less reliant on "just auto-generate everything and dump it in a big pile".

Start by reviewing the linked Sphinx issue #1609 and the repository's auto-generated documentation tree. Determine where enum members are expected to appear and whether the current documentation structure can support the change; done means enum members render correctly without relying on an unstructured generated dump.

索引モデルが issue の本文から書いたものです。