Review "hacks" and make plans for long-term stability, upstreaming

@agoose77 - this is an attempt at documenting some of the more severe workarounds and hacks in this code-base:

https://github.com/developmentseed/myst-anywidget-static-export/blob/main/docs/design-notes.md

I think that might be a good starting point to review / consider things that might be better fixed upstream, etc. Some of those points are lonboard-specific, and I can take those up separately in lonboard upstream.

(Please accept my perrenial, unconditional apology for the AI-generated docs there, but I'd be very happy to dig into any of those in greater detail with you, and also write out more thoughtfully if things seem vague)

I think for each of those "hacks", it would be great to start getting a sense of whether:
- It's fine to leave as is
- It should result in upstream work
- It is horrible and ghastly and we should find another approach

Read docs/design-notes.md first and review each listed workaround in the context of this TypeScript MyST static-export plugin. Done means recording whether each hack is acceptable, warrants upstream work, or needs replacement, while separating lonboard-specific items for follow-up upstream.

Written by the indexing model from the issue text.