feat: format multi-artist credits

internal/provider/yandex/client.go

@@ -564,7 +564,8 @@ func resultMap(resp map[string]any) map[string]any {
 func normalizeTrack(raw map[string]any, fallbackID string, artistSeparator string) map[string]any {
 	trackID := canonicalTrackRefFromRaw(raw, fallbackID)
 	albumRaw := firstAlbum(raw)
-	artistName := joinArtists(raw, artistSeparator)
+	artistNames := artistNames(raw)
+	artistName := displayArtistNames(artistNames)
 	albumArtist := joinAlbumArtists(albumRaw, artistSeparator)
 	if albumArtist == "" {
 		albumArtist = artistName
@@ -589,6 +590,7 @@ func normalizeTrack(raw map[string]any, fallbackID string, artistSeparator strin
 		"source_track_id":       jsonutil.StringFromAny(raw["realId"]),
 		"performer":             map[string]any{"name": artistName},
 		"artist":                map[string]any{"name": artistName, "id": firstArtistID(raw)},
+		"artist_names":          artistNames,
 		"album":                 normalizeAlbumSummary(albumRaw, albumArtist),
 		"image":                 imageMapFromTrack(raw, albumRaw),
 		"cover":                 imageMapFromTrack(raw, albumRaw),
@@ -769,6 +771,10 @@ func firstArtistID(raw map[string]any) string {
 }
 
 func joinArtists(raw map[string]any, artistSeparator string) string {
+	return displayArtistNames(artistNames(raw))
+}
+
+func artistNames(raw map[string]any) []string {
 	artists, _ := raw["artists"].([]any)
 	parts := make([]string, 0, len(artists))
 	for _, entry := range artists {
@@ -780,13 +786,17 @@ func joinArtists(raw map[string]any, artistSeparator string) string {
 			parts = append(parts, name)
 		}
 	}
-	return strings.Join(parts, artistSeparator)
+	return parts
 }
 
 func joinAlbumArtists(albumRaw map[string]any, artistSeparator string) string {
 	if len(albumRaw) == 0 {
 		return ""
 	}
+	return displayArtistNames(albumArtistNames(albumRaw))
+}
+
+func albumArtistNames(albumRaw map[string]any) []string {
 	artists, _ := albumRaw["artists"].([]any)
 	parts := make([]string, 0, len(artists))
 	for _, entry := range artists {
@@ -798,7 +808,20 @@ func joinAlbumArtists(albumRaw map[string]any, artistSeparator string) string {
 			parts = append(parts, name)
 		}
 	}
-	return strings.Join(parts, artistSeparator)
+	return parts
+}
+
+func displayArtistNames(names []string) string {
+	switch len(names) {
+	case 0:
+		return ""
+	case 1:
+		return names[0]
+	case 2:
+		return names[0] + " & " + names[1]
+	default:
+		return strings.Join(names[:len(names)-1], ", ") + " & " + names[len(names)-1]
+	}
 }
 
 func (c *Client) artistSeparator() string {