CLAUDE: Add printer_kvm.py — Ender 3 physical stylus control for phone touchscreen

Serial (USB/CH340G, 115200 baud) G-code driver for Creality Ender 3.
Provides tap(), swipe(), home(), calibrate() over /dev/ttyUSB0.
Part of the NanoKVM + Ender 3 physical phone-control project.
Co-authored-by: Claude <claude@elphel.com>