fix: improve Spotify importer metadata — copy iTunes durationMs, skip redundant backend lookup when frontend already enriched track

src/spotify.js

@@ -219,6 +219,7 @@ async function _loadSpotifyTrackArtwork(tracks, listEl) {
         if (match.trackNumber)        t.trackNumber        = match.trackNumber;
         if (match.trackExplicitness)  t.trackExplicitness  = match.trackExplicitness;
         if (match.previewUrl)         t.previewUrl         = match.previewUrl;
+        if (match.trackTimeMillis)    t.durationMs         = match.trackTimeMillis;
         if (window._spotifyResolved?.tracks?.[idx]) Object.assign(window._spotifyResolved.tracks[idx], t);
         const url = match.artworkUrl100 || match.artworkUrl60 || '';
         if (url) _setArt(artEls[idx], url);