[feat](trx-frontend-http): add auto-squelch button to Audio panel

Add an "Auto" button next to the SQL slider that sets the squelch
threshold to the current noise floor (estimated from spectrum bins)
plus a 6 dB margin. Uses the existing estimateNoiseFloorDb() heuristic.

https://claude.ai/code/session_01TDQyrZiPKfWGATVWPsLmHT
Signed-off-by: Claude <noreply@anthropic.com>

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

@@ -7669,6 +7669,29 @@ if (sdrSquelchEl) {
   });
 }
 
+const sdrSquelchAutoBtn = document.getElementById("sdr-squelch-auto");
+if (sdrSquelchAutoBtn) {
+  sdrSquelchAutoBtn.addEventListener("click", () => {
+    if (!sdrSquelchSupported) return;
+    const data = lastSpectrumData || window.lastSpectrumData;
+    if (!data || !Array.isArray(data.bins) || data.bins.length === 0) return;
+    const noiseDb = estimateNoiseFloorDb(data.bins);
+    if (noiseDb == null || !Number.isFinite(noiseDb)) return;
+    // Set threshold slightly above noise floor so squelch closes on noise
+    const thresholdDb = noiseDb + 6;
+    const clamped = Math.max(SDR_SQUELCH_MIN_DB, Math.min(SDR_SQUELCH_MAX_DB, thresholdDb));
+    const pct = clampSdrSquelchPercent(
+      ((clamped - SDR_SQUELCH_MIN_DB) / (SDR_SQUELCH_MAX_DB - SDR_SQUELCH_MIN_DB)) * 100,
+    );
+    if (sdrSquelchEl) {
+      sdrSquelchEl.value = String(pct);
+      updateSdrSquelchPctLabel();
+      saveSetting("sdrSquelchPct", pct);
+    }
+    submitSdrSquelchPercent(pct);
+  });
+}
+
 if (wfmAudioModeEl) {
   wfmAudioModeEl.value = loadSetting("wfmAudioMode", "stereo");
   wfmAudioModeEl.addEventListener("change", () => {

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -374,7 +374,7 @@
                 <button id="tx-audio-btn" type="button">Transmit Audio</button>
                 <label class="vol-label">RX<input type="range" id="rx-vol" min="0" max="100" value="80" class="vol-slider" /><small class="vol-pct" id="rx-vol-pct">80%</small></label>
                 <label class="vol-label">TX<input type="range" id="tx-vol" min="0" max="100" value="80" class="vol-slider" /><small class="vol-pct" id="tx-vol-pct">80%</small></label>
-                <label class="vol-label" id="sdr-squelch-wrap" style="display:none;">SQL<input type="range" id="sdr-squelch" min="0" max="100" value="0" class="vol-slider" /><small class="vol-pct" id="sdr-squelch-pct">Open</small></label>
+                <label class="vol-label" id="sdr-squelch-wrap" style="display:none;">SQL<input type="range" id="sdr-squelch" min="0" max="100" value="0" class="vol-slider" /><small class="vol-pct" id="sdr-squelch-pct">Open</small><button id="sdr-squelch-auto" type="button" class="sql-auto-btn" title="Set squelch to current noise level">Auto</button></label>
                 <div id="audio-level">
                   <div id="audio-level-fill"></div>
                 </div>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -1277,6 +1277,15 @@ small { color: var(--text-muted); }
   color: var(--text-muted);
   line-height: 1;
 }
+.sql-auto-btn {
+  font-size: 0.68rem;
+  padding: 0 5px;
+  height: 1.2rem;
+  min-height: 0;
+  line-height: 1;
+  border-radius: 3px;
+  cursor: pointer;
+}
 .vol-slider {
   -webkit-appearance: none;
   appearance: none;