Local dashboard: plain-language status checklist and C2-free listening

- /api/health: ordered checklist (password, C2 approval, MQTT, SDR, source,
  OP25, decoding, audio, Icecast) with what's wrong and what to do; pure
  build_checks() so every state (incl. Toughny's unapproved node) is tested
- /api/listen: pick P25 control channels / one analog freq / a cached C2
  system, validated in MHz, stored as a local override; OP25 restarted with
  the start failure reason surfaced
- /api/config/system no longer writes a raw blob OP25 can't read
- OP25 resumes after reboot on a locally chosen system, not only C2-assigned
- op25-container: analog (NBFM) config generation fixed (AttributeError +
  wrong field names), /op25/log tail, start refuses without a config,
  status detects a dead multi_rx ("crashed") -- node-26#12
- index.html rebuilt on UI_REDESIGN tokens; scanner drops DMR, shows System key

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

op25-container/run_multi-rx_service.sh

@@ -19,4 +19,13 @@ LIQ_PID=$! # Store the PID of the op25.liq process
 # until multi_rx.py is externally stopped (via the API).
 # The trap command ensures that SIGTERM is passed to the background jobs.
 trap "kill $MULTI_RX_PID $LIQ_PID" SIGTERM SIGINT
-wait $MULTI_RX_PID
+wait $MULTI_RX_PID
+RC=$?
+
+# multi_rx is gone (crashed, or SDR could not be opened). Take liquidsoap down
+# with it so nothing in this process group outlives the decoder — a leftover
+# liquidsoap kept /op25/status reporting "running" (node-26#12) and held the
+# Icecast mount against the next start.
+echo "multi_rx.py exited (code $RC) — stopping liquidsoap."
+kill $LIQ_PID 2>/dev/null
+exit $RC