Dark mode favicon for Panel#383

Currently in browsers that support light/dark theming or other types of browser theming, the default Panel favicon doesn’t work well with dark colors.

Default Safari dark mode theme for example renders black Kirby logo on very dark grey background. It’s hard to find the tab based on the icon this way.

While I know we can theoretically switch to a custom icon in panel via options, this isn’t a solution for all who don’t want to.

If hard to achieve, maybe switch the the favicon used here in nolt which renders way better than the other one in this context.

Thanks for considering!

Already done in https://github.com/getkirby/kirby/pull/4691