P1 of the radio-ID plan. The node now reports `radios`, one
{radio, start, end} per transmission, on /upload and on call_end. Both go
through app/internal/radios.py into `radios` + `radio_ids` on the call doc.
/upload writes them before the pipeline starts, because call_end arrives
after it.
call_end also writes srcaddr now. Only call_start used to, and the node
usually learns the talker after call_start, so most calls kept None and the
correlator's srcaddr match rarely fired. /upload fills srcaddr from the
latest radio when the doc has none.
Older nodes send neither field; nothing is blanked.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
