Read pen and finger Pointer Events in the web shell (capture phase) instead of
eframe's touch handlers, which can't tell a pen from a finger and see every
touch twice. The pen drives the pointer with its pressure and hovers; fingers
are touch contacts for pinch, two-finger pan and undo/redo taps. Once a pen
has been seen (remembered in localStorage), a finger or a resting palm never
presses a tool on the canvas, and a pen landing cancels fingers already down.
A long press drops the tool press and opens the context menu.
The page no longer scrolls, zooms or selects under touch, and the canvas
stays inside the safe areas of a full-screen app.
gniax