Fix Track model to match Python reference

- R128: changed from JSONR128 float64 to R128 struct with i, tp, important_secs fields
  (Python R128 is an object, not a number)
- StorageID -> StorageDir with json tag storage_dir (Python API uses storage_dir)
- Lyrics: replaced TrackLyricsInfo with Lyrics (from supplement/lyrics.py) and
  TrackLyricsInfo (from track/lyrics_info.py with has_available_sync_lyrics,
  has_available_text_lyrics fields)
- Track.Lyrics field now maps to lyrics_info JSON key with TrackLyricsInfo type

internal/models/base.go

@@ -111,33 +111,69 @@ func (id JSONID) String() string {
 	return string(id)
 }
 
-// JSONR128 is a flexible R128 loudness normalization value that accepts both JSON numbers and objects.
-// The Yandex Music API sometimes returns r128 as a number (e.g., -23.5) and sometimes
-// as an object (e.g., {"value": -23.5}). JSONR128 accepts both and stores as float64.
-type JSONR128 float64
+// R128 represents EBU R 128 loudness normalization parameters.
+// The Yandex Music API returns this either as a number (e.g., -23.5) or as an object
+// with fields i, tp, important_secs.
+type R128 struct {
+	BaseModel
+	I              float64 `json:"i"`
+	Tp             float64 `json:"tp"`
+	ImportantSecs  int     `json:"important_secs"`
+}
 
 // UnmarshalJSON implements json.Unmarshaler, accepting both JSON numbers and objects.
-func (r *JSONR128) UnmarshalJSON(data []byte) error {
-	// Try float64 first
+func (r *R128) UnmarshalJSON(data []byte) error {
+	// Try float64 first (API sometimes returns just a number)
 	var f float64
 	if err := json.Unmarshal(data, &f); err == nil {
-		*r = JSONR128(f)
+		r.I = f
+		r.Tp = 0
+		r.ImportantSecs = 0
 		return nil
 	}
-	// Try object with "value" key
+	// Try object with fields i, tp, important_secs
 	var obj struct {
-		Value float64 `json:"value"`
+		I              float64 `json:"i"`
+		Tp             float64 `json:"tp"`
+		ImportantSecs  int     `json:"important_secs"`
 	}
-	if err := json.Unmarshal(data, &obj); err == nil {
-		*r = JSONR128(obj.Value)
-		return nil
+	if err := json.Unmarshal(data, &obj); err != nil {
+		return err
 	}
-	// Default to 0 if neither format works
-	*r = 0
+	r.I = obj.I
+	r.Tp = obj.Tp
+	r.ImportantSecs = obj.ImportantSecs
 	return nil
 }
 
-// Float64 returns the R128 value as a float64.
-func (r JSONR128) Float64() float64 {
-	return float64(r)
+// Float64 returns the integrated loudness (i) value as a float64.
+func (r R128) Float64() float64 {
+	return r.I
+}
+
+// DeJSON deserializes an R128 from JSON data.
+func (r *R128) DeJSON(data []byte, c ClientInterface) (Model, error) {
+	r128 := &R128{BaseModel: *NewBaseModel(c)}
+	if err := r128.UnmarshalJSON(data); err != nil {
+		return nil, err
+	}
+	return r128, nil
+}
+
+// DeList deserializes a list of R128 from JSON data.
+func (r *R128) DeList(data []byte, c ClientInterface) ([]Model, error) {
+	var rawList []json.RawMessage
+	if err := json.Unmarshal(data, &rawList); err != nil {
+		return nil, err
+	}
+
+	result := make([]Model, 0, len(rawList))
+	for _, item := range rawList {
+		r128 := &R128{BaseModel: *NewBaseModel(c)}
+		if err := r128.UnmarshalJSON(item); err != nil {
+			continue
+		}
+		result = append(result, r128)
+	}
+	return result, nil
 }