fix: playlist cover art, compilation tag, and year

- ripPlaylist/ripTrackCollection: pre-fetch playlist artwork once, embed in all tracks
- ripTrack: skip per-track album cover when playlist embed is provided
- buildTagMetadata: set COMPILATION=1 and year from playlist publish_date
- beatport: normalize playlistMetadata to include date fields for year extraction
- qobuz: normalize playlist image_rectangle to standard image map

internal/audio/tag/tagger.go

@@ -16,7 +16,9 @@ type Metadata struct {
 	Artist              string
 	Artists             []string
 	AlbumArtist         string
+	Compilation         bool
 	OmitDiscTags        bool
+	Year                int
 	TrackNumber         int
 	DiscNumber          int
 	TrackTotal          int
@@ -197,6 +199,12 @@ func toTags(meta Metadata) map[string]string {
 	if meta.DiscTotal > 0 {
 		tags["disctotal"] = strconv.Itoa(meta.DiscTotal)
 	}
+	if meta.Compilation {
+		tags["COMPILATION"] = "1"
+	}
+	if meta.Year > 0 {
+		tags["year"] = strconv.Itoa(meta.Year)
+	}
 	return tags
 }