feat: auto-enrich genre/label from Deezer for built-in providers

- Add GetExtendedMetadataByISRC function in deezer.go
  - Searches track by ISRC then fetches album extended metadata
- Call enrichment in DownloadWithExtensionFallback before built-in download
  - Only enriches if genre/label are empty and ISRC is available
  - Logs enrichment results for debugging

go_backend/deezer.go

@@ -766,6 +766,32 @@ func (c *DeezerClient) GetExtendedMetadataByTrackID(ctx context.Context, trackID
 	return c.GetAlbumExtendedMetadata(ctx, albumID)
 }
 
+// GetExtendedMetadataByISRC searches for a track by ISRC and fetches extended metadata (genre, label)
+func (c *DeezerClient) GetExtendedMetadataByISRC(ctx context.Context, isrc string) (*AlbumExtendedMetadata, error) {
+	if isrc == "" {
+		return nil, fmt.Errorf("empty ISRC")
+	}
+
+	// First, search for track by ISRC
+	track, err := c.SearchByISRC(ctx, isrc)
+	if err != nil {
+		return nil, fmt.Errorf("failed to find track by ISRC: %w", err)
+	}
+
+	// SpotifyID contains "deezer:123" format, extract the ID
+	deezerID := track.SpotifyID
+	if strings.HasPrefix(deezerID, "deezer:") {
+		deezerID = strings.TrimPrefix(deezerID, "deezer:")
+	}
+
+	if deezerID == "" {
+		return nil, fmt.Errorf("track found but no Deezer ID")
+	}
+
+	// Then fetch extended metadata using the Deezer track ID
+	return c.GetExtendedMetadataByTrackID(ctx, deezerID)
+}
+
 func (c *DeezerClient) getJSON(ctx context.Context, endpoint string, dst interface{}) error {
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
 	if err != nil {

go_backend/extension_providers.go

@@ -2,6 +2,7 @@
 package gobackend
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -943,6 +944,27 @@ func DownloadWithExtensionFallback(req DownloadRequest) (*DownloadResponse, erro
 		GoLog("[DownloadWithExtensionFallback] Trying provider: %s\n", providerID)
 
 		if isBuiltInProvider(providerID) {
+			// For built-in providers, enrich with Deezer metadata if not already present
+			if (req.Genre == "" || req.Label == "") && req.ISRC != "" {
+				GoLog("[DownloadWithExtensionFallback] Enriching extended metadata from Deezer for ISRC: %s\n", req.ISRC)
+				ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+				deezerClient := GetDeezerClient()
+				extMeta, err := deezerClient.GetExtendedMetadataByISRC(ctx, req.ISRC)
+				cancel()
+				if err == nil && extMeta != nil {
+					if req.Genre == "" && extMeta.Genre != "" {
+						req.Genre = extMeta.Genre
+						GoLog("[DownloadWithExtensionFallback] Genre from Deezer: %s\n", req.Genre)
+					}
+					if req.Label == "" && extMeta.Label != "" {
+						req.Label = extMeta.Label
+						GoLog("[DownloadWithExtensionFallback] Label from Deezer: %s\n", req.Label)
+					}
+				} else if err != nil {
+					GoLog("[DownloadWithExtensionFallback] Failed to get extended metadata from Deezer: %v\n", err)
+				}
+			}
+
 			// Use built-in provider
 			result, err := tryBuiltInProvider(providerID, req)
 			if err == nil && result.Success {