Added support for the XVF3800 per-LED command LED_RING_COLOR (12-LED ring, 48-byte payload).
Implemented/readied the device control logic so the backend can:
write per-LED frames (set_ring_rgb / set_ring_solid / clear_ring),
detect availability (supports_per_led) and fall back if unsupported.
Improved robustness/diagnostics for USB control transfers (more consistent request composition + debug logging around writes).