Manual dark mode selection

[Floppy]

At the moment we can't do both automatic and manual dark mode selection; hopefully Bootstrap 6 will provide that option.

Hey, sorry, I know this is outdataed and closed, but was there a possibility to change from bright to darkmode with a switch inside manyfold somewhere (so not by changing it on the Browser/OS level). Thanks :)

Originally posted by @beniroquai in https://github.com/manyfold3d/manyfold/issues/2299#issuecomment-2395198983