Calls: store every radio heard on a call; call_end writes srcaddr (server-26#304)

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>

drb-c2-core/app/internal/mqtt_handler.py

@@ -6,6 +6,7 @@ import paho.mqtt.client as mqtt
 from app.config import settings
 from app.internal.logger import logger
 from app.internal import firestore as fstore
+from app.internal import radios
 from app.internal import talkgroups
 from app.internal.tenancy import FOUNDING_ORG_ID
 
@@ -307,6 +308,12 @@ class MQTTHandler:
             updates["org_id"] = node["org_id"]
         if payload.get("audio_url"):
             updates["audio_url"] = payload["audio_url"]
+        # The node usually learns the talker after call_start went out; only
+        # call_start used to write srcaddr, so most calls kept None
+        # (server-26#304).
+        if payload.get("srcaddr") is not None:
+            updates["srcaddr"] = payload["srcaddr"]
+        updates.update(radios.call_fields(payload.get("radios")))
 
         await fstore.doc_set("calls", call_id, updates)
         logger.info(f"Call end: {call_id}")