fix: clip label and screen-reader announcement use one identical string

The clip bar's visible label and its aria-live announcement were two
different formats ("17:09:56 to 17:09:57 (30 / 426)" vs "Clip 368 of
426: 21:25:44 to 21:25:50"). Build one string and use it for both, and
include the section's dB prominence (as the highlight chips do):

  17:09:56 to 17:09:57 · +30 dB (30 / 426)

The dB moves out of the hover tooltip into the spoken/visible label.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

webui.html

@@ -363,18 +363,21 @@ function playClip(i) {
         + '&start=' + cs.toFixed(1) + '&end=' + ce.toFixed(1);
   a.play().catch(() => {});
   // Label = wall-clock time of occurrence (absStart from the filename clock);
-  // falls back to in-file offsets for non-standard filenames.
+  // falls back to in-file offsets for non-standard filenames. The visible
+  // label and the screen-reader announcement use one identical string:
+  // "17:09:56 to 17:09:57 · +30 dB (30 / 426)".
   const when = c.absStart != null
     ? `${fmtClock(c.absStart)} to ${fmtClock(c.absStart + (c.end - c.start))}`
     : `${fmtDur(c.start)} to ${fmtDur(c.end)}`;
+  const score = c.score != null ? ` · +${Math.round(c.score)} dB` : '';
+  const text  = `${when}${score} (${i + 1} / ${clipQueue.length})`;
   const label = document.getElementById('clip-label');
-  label.textContent = `${when} (${i + 1} / ${clipQueue.length})`;
-  label.title = `${c.filename} @ ${fmtDur(c.start)}–${fmtDur(c.end)}`
-    + (c.score != null ? ` · +${Math.round(c.score)} dB` : '');
+  label.textContent = text;
+  label.title = `${c.filename} @ ${fmtDur(c.start)}–${fmtDur(c.end)}`;
   document.getElementById('clip-bar').hidden = false;
   document.body.classList.add('clip-open');
   setCutFields(c.fileIdx, c.start, c.end);
-  announce(`Clip ${i + 1} of ${clipQueue.length}: ${when}`);
+  announce(text);
 }
 
 function hideClipBar() {