[feat](trx-frontend-http): add clickable Sig Strength field between Wavelength and Frequency

Add a new "Sig Strength" display field in the freq row that shows
the measured signal strength. Clicking the field cycles through
three units: dBFS (default), dBf, and dBm. The selected unit is
persisted in localStorage.

https://claude.ai/code/session_01EvRV8UgsVtbrcH4t2hmFBF
Signed-off-by: Claude <noreply@anthropic.com>

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

@@ -307,6 +307,7 @@ function applyCapabilities(caps) {
 const freqEl = document.getElementById("freq");
 const centerFreqEl = document.getElementById("center-freq");
 const wavelengthEl = document.getElementById("wavelength");
+const sigStrengthEl = document.getElementById("sig-strength");
 const modeEl = document.getElementById("mode");
 const bandLabel = document.getElementById("band-label");
 const powerBtn = document.getElementById("power-btn");
@@ -573,6 +574,38 @@ let lastRendered = null;
 let hintTimer = null;
 let sigMeasuring = false;
 let sigLastSUnits = null;
+let sigLastDbm = null;
+const SIG_STRENGTH_UNITS = ["dBFS", "dBf", "dBm"];
+let sigStrengthUnitIdx = loadSetting("sigStrengthUnit", 0);
+
+function formatSigStrength(dbm) {
+  if (!Number.isFinite(dbm)) return "--";
+  const unit = SIG_STRENGTH_UNITS[sigStrengthUnitIdx] || "dBFS";
+  if (unit === "dBm") return `${dbm} dBm`;
+  if (unit === "dBf") {
+    // dBf = dBm + 107 (referenced to 1 femtowatt across 50 Ω)
+    const dbf = dbm + 107;
+    return `${dbf.toFixed(0)} dBf`;
+  }
+  // dBFS: map receiver range to a full-scale reference
+  // Typical receiver: -140 dBm (noise floor) to 0 dBm (full scale)
+  const dbfs = Math.max(-140, Math.min(0, dbm));
+  return `${dbfs} dBFS`;
+}
+
+function refreshSigStrengthDisplay() {
+  if (!sigStrengthEl) return;
+  sigStrengthEl.textContent = formatSigStrength(sigLastDbm);
+}
+
+if (sigStrengthEl) {
+  sigStrengthEl.addEventListener("click", () => {
+    sigStrengthUnitIdx = (sigStrengthUnitIdx + 1) % SIG_STRENGTH_UNITS.length;
+    saveSetting("sigStrengthUnit", sigStrengthUnitIdx);
+    refreshSigStrengthDisplay();
+  });
+}
+
 let sigMeasureTimer = null;
 let sigMeasureLastTickMs = 0;
 let sigMeasureAccumMs = 0;
@@ -3217,13 +3250,17 @@ function render(update) {
   if (update.status && update.status.rx && typeof update.status.rx.sig === "number") {
     const sUnits = dbmToSUnits(update.status.rx.sig);
     sigLastSUnits = sUnits;
+    sigLastDbm = update.status.rx.sig;
     const pct = sUnits <= 9 ? Math.max(0, Math.min(100, (sUnits / 9) * 100)) : 100;
     signalBar.style.width = `${pct}%`;
     signalValue.textContent = formatSignal(sUnits);
+    refreshSigStrengthDisplay();
   } else {
     sigLastSUnits = null;
+    sigLastDbm = null;
     signalBar.style.width = "0%";
     signalValue.textContent = "--";
+    refreshSigStrengthDisplay();
   }
   if (bandLabel) {
     bandLabel.textContent = typeof update.band === "string" ? update.band : "--";

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

@@ -176,6 +176,10 @@
             <div class="wavelength-display" id="wavelength" title="Wavelength">--</div>
             <div class="label"><span>Wavelength</span></div>
           </div>
+          <div class="freq-field sig-strength-col">
+            <div class="sig-strength-display" id="sig-strength" title="Click to change unit">--</div>
+            <div class="label"><span>Sig Strength</span></div>
+          </div>
           <div class="freq-field frequency-col">
             <input class="status-input" id="freq" type="text" value="--" />
             <div class="label"><span>Frequency</span></div>

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

@@ -550,6 +550,9 @@ button:disabled { opacity: 0.6; cursor: not-allowed; }
 .wavelength-col {
   flex: 0 0 auto;
 }
+.sig-strength-col {
+  flex: 0 0 auto;
+}
 .unit-col {
   flex: 0 0 auto;
 }
@@ -625,6 +628,26 @@ button:disabled { opacity: 0.6; cursor: not-allowed; }
   white-space: nowrap;
   flex-shrink: 0;
 }
+.sig-strength-display {
+  min-width: 5.2rem;
+  height: 3.35rem;
+  padding: 0 0.7rem;
+  border: 1px solid var(--border-light);
+  border-radius: 6px;
+  background: var(--input-bg);
+  color: var(--wavelength-fg);
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  font-family: 'DSEG14 Classic', monospace;
+  font-weight: 600;
+  font-size: 1.25rem;
+  letter-spacing: 0.03em;
+  white-space: nowrap;
+  flex-shrink: 0;
+  cursor: pointer;
+  user-select: none;
+}
 small { color: var(--text-muted); }
 .header {
   margin-bottom: 0;
@@ -2747,11 +2770,13 @@ button:focus-visible, input:focus-visible, select:focus-visible {
     min-width: 0;
   }
   .wavelength-col,
+  .sig-strength-col,
   .unit-col,
   .mult-col {
     min-width: 0;
   }
   .wavelength-display,
+  .sig-strength-display,
   .jog-step,
   .jog-mult {
     width: 100%;