the main canvas is now DPI-aware; it should no longer be pixelated on 4k
this couldn't be done for the brush preview, so it's just kinda pixelated
also fixed the horrendous scrollbar that could appear on HiDPI for some reason
for faster load times, and seamless updates.
because for some reason ServeDir can't do it correctly, and it tells the client "yeah hey nothing changed" even if something changed
this is quite common in other apps with an infinite canvas - such as Miro
also on laptops middle-clicking is a pain in the ass, though we should add more proper touchpad support for that case