Extends the existing XVF3800 USB control backend beyond LEDs to support startup preflight commands needed for audio reliability.
Implements command execution internally (no reliance on xvf_host.py) using the same USB control-transfer approach already used for LED features.
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).