The signal probe now sends a zero-hop NODE_DISCOVER_REQ control packet
(the standard MeshCore node-discovery that the Ultra / KiekR apps use)
instead of a trace, which repeaters do not answer. Repeaters reply
directly with a NODE_DISCOVER_RESP, captured in onControlDataRecv by
matching the probe tag into _ui_sig_* SNR/RSSI. Thanks to Tarmo for
decoding the exact packet.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
