v0.4.1 — remote control

Remote control

COMPUTER_USE_REMOTE_CONTROL=1 turns one process into a remote-desktop
driver: click, right_click, drag, hover and scroll move the machine's
real cursor, and type_text / press_key go to whatever is focused — the way
Chrome Remote Desktop or Screen Sharing behave.

Everything else is unchanged. Without the flag this server still keeps its
hands off the pointer: coordinate clicks are routed to one window, keystrokes
are posted to one process, and an untargetable action is refused rather than
taking over the machine, so an agent can work while you keep using your
computer. A host that runs both an agent and a viewer runs them as two
processes.

• scroll now takes optional x/y, so the wheel acts over the point the
  viewer scrolled at (remote control only; ignored otherwise).
• The agent-cursor overlay stays hidden in remote control — there is one
  pointer now, and it is the real one.