Documentation site overhaul

[gwhitney]

The second PR disrupted the styling of the documentation pages; we need to get them to correspond to the overall styling of the app again.

Originally posted by @gwhitney in https://github.com/numberscope/admin/discussions/6#discussioncomment-9886650

[gwhitney]

This should also encompass #320, #319, #221, #179, #46.

[gwhitney]

Kate points out "the doc file behind-the-scenes.md is probably out of date after delft".

[gwhitney]

Associated PR merged; closing.