feat(track): show now-playing bars overlay on cover art

Overlay the accent-coloured "hopping bars" PlayingIndicator on a
track's cover art wherever TrackRow appears when it's the active
player track, and reuse the same component/overlay for the current
entry's cover in the queue panel.

src/components/track/TrackRow.tsx

@@ -4,6 +4,7 @@ import { TrackContextMenu } from './TrackContextMenu';
 import { AvailabilityBadge } from './AvailabilityBadge';
 import { MetadataStatusBadge } from './MetadataStatusBadge';
 import { Icon } from '../common/Icon';
+import { PlayingIndicator } from '../common/PlayingIndicator';
 import { formatDuration } from '../../lib/format';
 import { useAppDispatch, useAppSelector } from '../../hooks/useAppDispatch';
 import { playNow } from '../../store/slices/queue';
@@ -73,10 +74,7 @@ export function TrackRow({
       >
         {isActive && isPlaying ? '▶' : index !== undefined ? index + 1 : ''}
       </span>
-      <div
-        className="track-art"
-        style={{ position: 'relative', width: 36, height: 36 }}
-      >
+      <div className="track-art">
         {artUrl ? (
           <img
             src={artUrl}
@@ -95,6 +93,11 @@ export function TrackRow({
             }}
           />
         )}
+        {isActive && (
+          <div className="cover-playing">
+            <PlayingIndicator animate={isPlaying} />
+          </div>
+        )}
         <button
           type="button"
           className="track-art-play"