feat: extract embedded album artwork during scans

Add a dedicated artwork cache directory and save embedded album art from audio tags during library scans. Prefer embedded artwork for album cover resolution while keeping sidecar image files as the fallback path.

internal/scanner/service.go

@@ -38,6 +38,7 @@ type Result struct {
 type Service struct {
 	db        *sql.DB
 	mediaRoot string
+	artworkRoot string
 	mu        sync.RWMutex
 	status    Status
 }
@@ -78,8 +79,8 @@ type scannedTrack struct {
 	ContentType  string
 }
 
-func NewService(db *sql.DB, mediaRoot string) *Service {
-	return &Service{db: db, mediaRoot: mediaRoot}
+func NewService(db *sql.DB, mediaRoot, artworkRoot string) *Service {
+	return &Service{db: db, mediaRoot: mediaRoot, artworkRoot: artworkRoot}
 }
 
 func (s *Service) HasMediaFiles() bool {
@@ -327,7 +328,13 @@ func (s *Service) scanFile(path string) (scannedItem, error) {
 	artistID := hashID("artist", artistName)
 	albumID := hashID("album", artistName, albumTitle, fmt.Sprintf("%d", year))
 	trackID := hashID("track", path)
-	coverArt := findCoverArt(filepath.Dir(path))
+	coverArt := ""
+	if err == nil {
+		coverArt = s.extractEmbeddedCoverArt(metadata, albumID)
+	}
+	if coverArt == "" {
+		coverArt = findCoverArt(filepath.Dir(path))
+	}
 
 	return scannedItem{
 		artist: scannedArtist{
@@ -417,6 +424,44 @@ func findCoverArt(dir string) string {
 	return ""
 }
 
+func (s *Service) extractEmbeddedCoverArt(metadata tag.Metadata, albumID string) string {
+	if metadata == nil {
+		return ""
+	}
+
+	picture := metadata.Picture()
+	if picture == nil || len(picture.Data) == 0 {
+		return ""
+	}
+
+	if s.artworkRoot == "" {
+		return ""
+	}
+
+	if err := os.MkdirAll(s.artworkRoot, 0o755); err != nil {
+		return ""
+	}
+
+	filename := albumID + coverExtension(picture.MIMEType)
+	path := filepath.Join(s.artworkRoot, filename)
+	if err := os.WriteFile(path, picture.Data, 0o644); err != nil {
+		return ""
+	}
+
+	return path
+}
+
+func coverExtension(mimeType string) string {
+	switch strings.ToLower(mimeType) {
+	case "image/png":
+		return ".png"
+	case "image/webp":
+		return ".webp"
+	default:
+		return ".jpg"
+	}
+}
+
 func (s *Service) tryMarkStarted() bool {
 	s.mu.Lock()
 	defer s.mu.Unlock()