toc without highlighting and without mobile view

[cinxmo]

Quick and simple TOC without the following:

• highlighting the section the user is on as the user is scrolling. see implementation in client.js here using a doubly linked list to keep track of the prev, current, and next sections. It could be too slow to react to a scroll event every single time to determine which section should be highlighted.
• mobile view - should have hamburger menu, etc. right now it just hides the toc. for simplicity, let's have this merged in first.

[cinxmo]

do we want to follow the exact same naming as Vitepress? I think we should opt for something different

[Fil]

this is the override test, it needs to be different from the new default which is "Contents"

[Fil]

We discussed fast-follows:

• responsive mode (small screens), maybe with a hamburger (css) and tracking width changes in JS
• test on iPhone and iPad (easy, maybe use ngrok)
• use IntersectionObserver to highlight the current section (hard!)

This css rule will show a hamburger next to (or instead of) the toc header:

#observablehq-toc summary::before  {
 content: '☰ ';
}