Add stylus pressure-sensitivity support on macOS

[guidocelada]

I’m using the app on macOS with a graphics tablet (no screen) that supports pen pressure, but the app currently treats all strokes the same.

It would be great if the app could read pressure input (line weight / opacity / brush size). This would make sketching and note-taking much more natural.

If you need testing on macOS, happy to help.

Thanks!