Commands:
PSET x,y,r,g,b — set one pixel
LINE x1,y1,x2,y2,r,g,b — Bresenham line (colour optional, uses current)
CIRCLE cx,cy,radius,r,g,b — circle (colour optional)
CLS [r,g,b] — clear screen (colour optional, default black)
DEMO — bulk pixel write demo
Mouse: click or drag to draw with current colour
Hover: reads pixel value + buffer byte offset live