feat(album): single cover on album detail, track-number rows

Album detail header falls back to a track's cover when the album
record itself has none, and each track row hides its per-track art in
favour of a large album-position number, since the header already
shows the album's cover once.

src/components/track/TrackRow.tsx

@@ -15,6 +15,10 @@ interface Props {
   track: Track;
   index?: number;
   showAlbum?: boolean;
+  /** Hide cover art and show the track's album position instead — used on
+   * the album detail page, where the album cover is already shown once in
+   * the header and per-track art would be redundant. */
+  hideArt?: boolean;
   onAddToPlaylist?: (track: Track) => void;
   onEditMetadata?: (track: Track) => void;
   onDelete?: (track: Track) => void;
@@ -24,6 +28,7 @@ export function TrackRow({
   track,
   index,
   showAlbum = false,
+  hideArt = false,
   onAddToPlaylist,
   onEditMetadata,
   onDelete,
@@ -58,24 +63,43 @@ export function TrackRow({
       selected={isActive}
       style={{
         display: 'grid',
-        gridTemplateColumns: '2rem 2.5rem 1fr auto auto',
+        gridTemplateColumns: hideArt
+          ? '2.5rem 1fr auto auto'
+          : '2rem 2.5rem 1fr auto auto',
         gap: '0.75rem',
         alignItems: 'center',
         padding: '0.375rem 0.75rem',
         cursor: 'default',
       }}
     >
-      <span
-        style={{
-          fontSize: '0.75rem',
-          color: 'var(--color-text-3)',
-          textAlign: 'right',
-        }}
-      >
-        {isActive && isPlaying ? '▶' : index !== undefined ? index + 1 : ''}
-      </span>
+      {!hideArt && (
+        <span
+          style={{
+            fontSize: '0.75rem',
+            color: 'var(--color-text-3)',
+            textAlign: 'right',
+          }}
+        >
+          {isActive && isPlaying ? '▶' : index !== undefined ? index + 1 : ''}
+        </span>
+      )}
       <div className="track-art">
-        {artUrl ? (
+        {hideArt ? (
+          <div
+            style={{
+              width: 36,
+              height: 36,
+              display: 'flex',
+              alignItems: 'center',
+              justifyContent: 'center',
+              fontSize: '1.0625rem',
+              fontWeight: 600,
+              color: isActive ? 'var(--color-accent)' : 'var(--color-text-3)',
+            }}
+          >
+            {track.trackNumber ?? (index !== undefined ? index + 1 : '')}
+          </div>
+        ) : artUrl ? (
           <img
             src={artUrl}
             alt=""