[mister-teddy]

Follow-up to #6: these commits landed on its branch after it was merged.

• sudo, su and passwd work for the desktop user: they get their setuid bit back, with a one-time repair on existing installs.
• A mouse plugged into the phone moves the cursor on the external display, not on the phone, and clicks and scrolls there.
• The mouse wheel and two-finger scrolling work in X apps (the compositor now reports relative pointer motion, so Xwayland keeps one pointer device).
• The logo sits in the top left of the trackpad, with the same gap to the border as the buttons in the top right.
• Connecting a keyboard offers the keyboard shortcuts service, so Alt+Tab goes to the desktop instead of switching phone apps. The prompt is shorter and opens Settings with our entry highlighted.
• Black instead of red behind the desktop while the screen rotates.

Same changes in Local Desktop: localdesktop/localdesktop.github.io#348