Ryan Malloy 7f1e0cf0d7 Add USB serial transport for HMC472A attenuator control
HMC472ASerial class implements usb-serial-json-v1 protocol over the
ESP32-S3's native USB CDC port. Auto-detection scans /dev/ttyACM* and
probes with the identify command to find the right port.

--attenuator flag now defaults to 'auto' (USB first, HTTP fallback).
Also accepts direct serial port paths or HTTP URLs for explicit control.
2026-02-18 15:06:00 -07:00
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