feat: add lyrics source tracking, Paxsenix partner, and dedicated lyrics provider settings page

- Add getLyricsLRCWithSource to return lyrics with source metadata
- Display lyrics source in track metadata screen
- Improve LRC parsing to preserve background vocal tags
- Add dedicated LyricsProviderPriorityPage for provider configuration
- Add Paxsenix as lyrics proxy partner for Apple Music/QQ Music
- Handle inline timestamps and speaker prefixes in LRC display

go_backend/exports.go

@@ -1008,6 +1008,64 @@ func GetLyricsLRC(spotifyID, trackName, artistName string, filePath string, dura
 	return lrcContent, nil
 }
 
+func GetLyricsLRCWithSource(spotifyID, trackName, artistName string, filePath string, durationMs int64) (string, error) {
+	if filePath != "" {
+		lyrics, err := ExtractLyrics(filePath)
+		if err == nil && lyrics != "" {
+			result := map[string]interface{}{
+				"lyrics":       lyrics,
+				"source":       "Embedded",
+				"sync_type":    "EMBEDDED",
+				"instrumental": false,
+			}
+			jsonBytes, err := json.Marshal(result)
+			if err != nil {
+				return "", err
+			}
+			return string(jsonBytes), nil
+		}
+
+		result := map[string]interface{}{
+			"lyrics":       "",
+			"source":       "",
+			"sync_type":    "",
+			"instrumental": false,
+		}
+		jsonBytes, err := json.Marshal(result)
+		if err != nil {
+			return "", err
+		}
+		return string(jsonBytes), nil
+	}
+
+	client := NewLyricsClient()
+	durationSec := float64(durationMs) / 1000.0
+	lyricsData, err := client.FetchLyricsAllSources(spotifyID, trackName, artistName, durationSec)
+	if err != nil {
+		return "", err
+	}
+
+	lrcContent := ""
+	if lyricsData.Instrumental {
+		lrcContent = "[instrumental:true]"
+	} else {
+		lrcContent = convertToLRCWithMetadata(lyricsData, trackName, artistName)
+	}
+
+	result := map[string]interface{}{
+		"lyrics":       lrcContent,
+		"source":       lyricsData.Source,
+		"sync_type":    lyricsData.SyncType,
+		"instrumental": lyricsData.Instrumental,
+	}
+	jsonBytes, err := json.Marshal(result)
+	if err != nil {
+		return "", err
+	}
+
+	return string(jsonBytes), nil
+}
+
 func EmbedLyricsToFile(filePath, lyrics string) (string, error) {
 	err := EmbedLyrics(filePath, lyrics)
 	if err != nil {

go_backend/lyrics.go

@@ -608,6 +608,13 @@ func parseSyncedLyrics(syncedLyrics string) []LyricsLine {
 			continue
 		}
 
+		// Preserve Apple/QQ background vocal tags by attaching them to
+		// the previous timed line. This keeps [bg:...] in final exported LRC.
+		if strings.HasPrefix(line, "[bg:") && len(lines) > 0 {
+			lines[len(lines)-1].Words = strings.TrimSpace(lines[len(lines)-1].Words + "\n" + line)
+			continue
+		}
+
 		matches := lrcPattern.FindStringSubmatch(line)
 		if len(matches) == 5 {
 			startMs := lrcTimestampToMs(matches[1], matches[2], matches[3])

go_backend/lyrics_apple.go

@@ -289,7 +289,7 @@ func formatPaxContent(lyricsType string, content []paxLyrics, multiPersonWordByW
 
 		timestamp := msToLRCTimestamp(int64(line.Timestamp))
 
-		if lyricsType == "Syllable" {
+		if strings.EqualFold(lyricsType, "Syllable") {
 			sb.WriteString(timestamp)
 			if multiPersonWordByWord {
 				if line.OppositeTurn {