Dark Mode

[mattloose]

If we are going to have dark mode it should - at least - work...

• [x] check each page for correct dark mode performance
• [ ] check each graph for readability
• [ ] remove shadow styling where appropriate

[mattloose]

Dark mode is checked on each page as of #fix/darkmode

Graph readability is more complex and is challenging in nicegui currently - see https://github.com/zauberzeug/nicegui/issues/3753#issuecomment-2383175848 for some further discussion of tailwind issues in dark mode.