fix: show duration overlay on asset cards using duration_ms

asset.duration is not a DB field — it's duration_ms (milliseconds).
Divide by 1000 before passing to formatDuration() which expects seconds.

services/web-ui/public/index.html

@@ -699,7 +699,7 @@
           <img data-asset-id="${asset.id}" alt="${escHtml(asset.display_name || asset.filename)}" aria-hidden="false">
           <div class="asset-thumb-overlay">
             <span class="badge ${statusClass}">${escHtml(asset.status)}</span>
-            ${asset.duration ? `<span class="asset-duration">${formatDuration(asset.duration)}</span>` : ''}
+            ${asset.duration_ms ? `<span class="asset-duration">${formatDuration(asset.duration_ms / 1000)}</span>` : ''}
           </div>
           <div class="asset-actions">
             <button class="asset-action-btn" onclick="openInEditor('${asset.id}', event)" title="Open in Editor">