Add vesc_mqtt_relay_node.py to saltybot_phone: subscribes to
/vesc/left/state, /vesc/right/state, /vesc/combined ROS2 topics and
publishes JSON telemetry to saltybot/phone/vesc_{left,right,combined}
MQTT topics at 5 Hz per motor. 32 unit tests, no ROS2/paho required.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>