Make sidebar list item foldable on API Reference page on the document

[mehm8128]

When we see https://valibot.dev/api/ , it is difficult to find what we want to see on the sidebar. So, I want each item of sidebar(Schemas, Methods, Actions, etc.) to be foldable. If this is implemented, sidebar is supposed to be like below screenshot with clickable button(yet not exist in screenshot) which can expand its items.