[feat](trx-frontend-http): display RDS PS name overlay on overview strip

When a WFM/SDR spectrum stream carries RDS data, show the Program
Service name (8-char station name) centered on the visible waveform
area in DSEG14 monospace — the same font as the frequency display.

- Add #rds-ps-overlay div inside .overview-strip (pointer-events: none,
  z-index: 2, absolutely positioned at the center of the visible canvas)
- updateRdsPsOverlay(rds) shows/hides and updates text on every spectrum
  frame; trims trailing spaces common in RDS PS strings
- Overlay cleared on spectrum disconnect / null frame
- text-shadow uses CSS color-mix against --bg for legibility across all
  style/theme combinations

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

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

@@ -330,6 +330,7 @@ const overviewPeakHoldEl = document.getElementById("overview-peak-hold");
 const themeToggleBtn = document.getElementById("theme-toggle");
 const headerRigSwitchSelect = document.getElementById("header-rig-switch-select");
 const headerStylePickSelect = document.getElementById("header-style-pick-select");
+const rdsPsOverlay = document.getElementById("rds-ps-overlay");
 let overviewPeakHoldMs = Number(loadSetting("overviewPeakHoldMs", 2000));
 
 let overviewDrawPending = false;
@@ -2793,6 +2794,7 @@ function startSpectrumStreaming() {
       overviewWaterfallRows = [];
       scheduleOverviewDraw();
       clearSpectrumCanvas();
+      updateRdsPsOverlay(null);
       return;
     }
     try {
@@ -2800,6 +2802,7 @@ function startSpectrumStreaming() {
       pushOverviewWaterfallFrame(lastSpectrumData);
       refreshCenterFreqDisplay();
       scheduleSpectrumDraw();
+      updateRdsPsOverlay(lastSpectrumData.rds);
     } catch (_) {}
   };
   spectrumSource.onerror = () => {
@@ -2824,6 +2827,7 @@ function stopSpectrumStreaming() {
   lastSpectrumData = null;
   overviewWaterfallRows = [];
   scheduleOverviewDraw();
+  updateRdsPsOverlay(null);
   clearSpectrumCanvas();
 }
 
@@ -2835,6 +2839,17 @@ function clearSpectrumCanvas() {
   ctx.fillRect(0, 0, spectrumCanvas.width, spectrumCanvas.height);
 }
 
+function updateRdsPsOverlay(rds) {
+  if (!rdsPsOverlay) return;
+  const ps = rds?.program_service?.trim();
+  if (ps) {
+    rdsPsOverlay.textContent = ps;
+    rdsPsOverlay.style.display = "";
+  } else {
+    rdsPsOverlay.style.display = "none";
+  }
+}
+
 function scheduleSpectrumDraw() {
   if (spectrumDrawPending) return;
   spectrumDrawPending = true;