New WebSocket endpoint streams real-time RGB frames from any CSS source.
Generic sources show a horizontal LED strip canvas. Picture sources show
a rectangle with per-edge canvases matching the calibration layout.
Server computes exact output indices per edge (offset + reverse + CW/CCW)
so the frontend renders edges in correct visual orientation.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
