[fix](trx-frontend): narrow weak WFM to 60 kHz

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -4268,7 +4268,7 @@ const MODE_BW_DEFAULTS = {
   FM:     [12_500, 2_500, 25_000, 500],
   AIS:    [25_000, 12_500, 50_000, 500],
   VDES:   [100_000, 25_000, 200_000, 1_000],
-  WFM:    [180_000, 50_000,300_000,5_000],
+  WFM:    [180_000, 60_000,300_000,5_000],
   DIG:    [3_000,  300,   6_000,  100],
   PKT:    [25_000, 300,  50_000,  500],
 };
@@ -4390,7 +4390,7 @@ function estimateOccupiedBandwidth(data, centerHz) {
   let peak = -Infinity;
   for (let i = searchLo; i <= searchHi; i++) peak = Math.max(peak, smoothed[i]);
   const snr = peak - noise;
-  if (!Number.isFinite(snr) || snr < (isWfm ? 5 : 4)) return defaultBw;
+  if (!Number.isFinite(snr) || snr < (isWfm ? 5 : 4)) return isWfm ? minBw : defaultBw;
 
   // A threshold relative to the noise floor finds occupied bandwidth much
   // more reliably than one relative to the peak.  The latter fails for WFM,
@@ -4424,10 +4424,10 @@ function estimateOccupiedBandwidth(data, centerHz) {
     rawBw = 2 * Math.max(leftHz, rightHz);
   }
 
-  // Add a transition-band margin. Reject implausibly narrow WFM measurements:
-  // they are normally a pilot/centre feature or a neighbouring narrow signal.
+  // Add a transition-band margin.  Weak WFM deliberately falls back to the
+  // 60 kHz mode floor above: a narrower filter trades stereo/RDS content for
+  // a useful improvement in intelligibility when the signal is very poor.
   rawBw *= isWfm ? 1.08 : 1.12;
-  if (isWfm && rawBw < defaultBw * 0.55) return defaultBw;
   const clamped = Math.max(minBw, Math.min(maxBw, rawBw));
   return Math.max(stepBw, Math.round(clamped / stepBw) * stepBw);
 }