feat(tci): receive audio over the TCI WebSocket (experimental)

A SunSDR already carries its receive audio on the same WebSocket as its
commands, so a virtual audio cable and a second sound card are two pieces
of plumbing an operator installs for no reason. This is the receive half:
what the QSO recorder and the CW decoder need.

The reader now looks at the frame type. It used to ignore it and split
every frame on ';' -- harmless only for as long as no stream was ever
opened, since audio bytes would otherwise have been handed to the command
parser a hundred times a second.

NOTHING HERE IS CONFIRMED ON A RADIO. The header layout comes from the
TCI documentation, and the stream-type numbers are exactly the sort of
detail a document gets right and a memory of it does not -- so the first
forty frames of a session are logged verbatim, and a test bench in
Preferences > Audio reports the sample rate the radio chose, the frames
arriving and the peak level of the last second. 'The stream is open' and
'audio is arriving' are different claims and only the second is worth
anything to whoever tries this first.

Transmit (the voice keyer) is the other half and is deliberately absent:
it has to answer the radio's chrono packets at the right pace, and that
is worth doing once the format is settled on real hardware.

frontend/src/components/SettingsModal.tsx

@@ -58,7 +58,7 @@ import {
   GetFolderSync, SaveFolderSync, PickFolderSyncFolder, GetFolderSyncStatus, SyncFolderNow,
   GetRelayAuto, SaveRelayAuto, GetStationDevices,
   GetAwardDefs, GetTrackedAwards, SaveTrackedAwards,
-  GetBandOpenSettings, SaveBandOpenSettings, GetGridScopeSettings, SaveGridScopeSettings, GetPSKReporterStatus, GetChaseNewGrids, SetChaseNewGrids, GetChaseNew, SetChaseNew, GetGridCacheStatus, GetLinkedAmps, SetLinkedAmps, GetSpotTTLMinutes, SetSpotTTLMinutes, GetSpotMax, SetSpotMax,
+  GetBandOpenSettings, SaveBandOpenSettings, GetGridScopeSettings, SaveGridScopeSettings, GetPSKReporterStatus, GetChaseNewGrids, SetChaseNewGrids, GetChaseNew, SetChaseNew, GetGridCacheStatus, GetLinkedAmps, SetLinkedAmps, GetSpotTTLMinutes, SetSpotTTLMinutes, GetSpotMax, SetSpotMax, StartTCIAudio, StopTCIAudio, GetTCIAudioStatus,
 } from '../../wailsjs/go/main/App';
 import type { profile as profileModels } from '../../wailsjs/go/models';
 import type { LookupSettingsForm, StationSettingsForm, ListsSettingsForm, ModePresetForm } from '@/types';
@@ -1943,6 +1943,15 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
   const [spotTTL, setSpotTTL] = useState(0);
   const [spotTTLText, setSpotTTLText] = useState('0');
   const [spotMaxText, setSpotMaxText] = useState('1000');
+  // TCI receive-audio test bench. Polled only while the stream is open: a panel
+  // that asks the backend twice a second for a stream nobody started is work
+  // done for nothing.
+  const [tciAudio, setTciAudio] = useState<any>({ running: false, sample_rate: 0, frames: 0, peak_db: -99 });
+  useEffect(() => {
+    if (!tciAudio.running) return;
+    const id = window.setInterval(() => { GetTCIAudioStatus().then(setTciAudio).catch(() => {}); }, 500);
+    return () => window.clearInterval(id);
+  }, [tciAudio.running]);
   const [gridStat, setGridStat] = useState<any>(null);
   const [pskrStatus, setPskrStatus] = useState<any>(null);
   const saveBandOpen = async (next: any) => {
@@ -6542,6 +6551,35 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
             <strong>{t('aud.fromRadioShort')}</strong> {t('aud.explainFrom')}{' '}
             <strong>{t('aud.toRadioShort')}</strong> {t('aud.explainTo')}
           </p>
+
+          {/* TCI receive audio — EXPERIMENTAL, and the panel says so.
+              A SunSDR already carries its receive audio on the WebSocket that
+              carries its commands, so none of the devices above need to exist
+              for it: no virtual cable, no second sound card. This is the test
+              bench for that path — it opens the stream and reports what really
+              arrives, because "the stream is open" and "audio is arriving" are
+              different claims and only the second one is worth anything. */}
+          <div className="rounded-md border border-border p-3 space-y-2">
+            <div className="text-xs font-medium">{t('aud.tciTitle')}</div>
+            <div className="flex items-center gap-3 flex-wrap">
+              <Button variant={tciAudio.running ? 'default' : 'outline'} size="sm" className="h-8"
+                onClick={() => {
+                  const p = tciAudio.running ? StopTCIAudio() : StartTCIAudio(0, 48000);
+                  p.then(() => GetTCIAudioStatus().then(setTciAudio))
+                   .catch((e: any) => setTciAudio((s: any) => ({ ...s, last_err: String(e?.message ?? e) })));
+                }}>
+                {tciAudio.running ? t('aud.tciStop') : t('aud.tciStart')}
+              </Button>
+              {tciAudio.running && (
+                <span className="text-[11px] font-mono text-muted-foreground">
+                  {tciAudio.sample_rate || 0} Hz · {tciAudio.frames || 0} frames ·{' '}
+                  {tciAudio.peak_db > -90 ? tciAudio.peak_db.toFixed(1) + ' dBFS' : t('aud.tciSilent')}
+                </span>
+              )}
+            </div>
+            {!!tciAudio.last_err && <p className="text-[11px] text-danger">{tciAudio.last_err}</p>}
+            <p className="text-[11px] text-muted-foreground">{t('aud.tciHint')}</p>
+          </div>
           <div className="flex items-center gap-3">
             <Button
               variant={monitorOn ? 'default' : 'outline'}