Add ability to change background color, to evaluate results

[Stokestack]

If you're tracing a dark image, it can hard to evaluate results in the preview pane. It would help to be able to set the background color, or at least toggle between light & dark.

Currently I'm not sure what the results window is showing, because it shows a highly speckled and indistinct image despite the output of the tool being a nice, crisp SVG (I was using a black-&-white mostly-text image).

This tool works well, nice job.

[tomayac]

I have a dark mode toggle ready to go, but am waiting for vitejs/vite#6748 to be fixed before I can use it. Thanks for the kind words!

[tomayac]

@Stokestack The dark mode toggle is now enabled and ready to go. Find it in the lower left corner of the side bar.

[Stokestack]

Great, I'll check it out! Thanks!