replace mkdocs with something

[Grotax]

It looks like mkdocs will no longer be maintained.

https://squidfunk.github.io/mkdocs-material/blog/2026/02/18/mkdocs-2.0/
https://fpgmaas.com/blog/collapse-of-mkdocs/

I think it is still to early to decide what to move to and so far it still builds.

We want for our docs:

• use markdown
• use a static page generator
• use GitHub pages

[SMillerDev]

I recently saw this one recommended, might be a good option: https://starlight.astro.build/