Fix ID fields to accept both JSON strings and numbers

The Yandex Music API returns IDs as both JSON strings and numbers depending
on the endpoint. Added JSONID custom type in internal/models/base.go that
implements json.Unmarshaler to accept both formats and store as string.

Changed ID fields from string to JSONID:
- Track.ID, Major.ID, TrackLyricsInfo.ID (track.go)
- Album.ID, TrailerInfo.TrackID, TrailerInfo.AlbumID (album.go)

Updated example to convert JSONID to string when passing to client methods.

Co-Authored-By: Claude Code <noreply@anthropic.com>

internal/models/track.go

@@ -8,7 +8,7 @@ import (
 // Track represents a full track from the Yandex Music API.
 type Track struct {
 	BaseModel
-	ID                       string           `json:"id"`
+	ID                       JSONID           `json:"id"`
 	Title                    string           `json:"title"`
 	DurationMs               int              `json:"duration_ms"`
 	StorageID                string           `json:"storage_id"`
@@ -149,14 +149,14 @@ func (t *Track) GetDownloadInfo(quality string) *DownloadInfo {
 
 // Major represents major label info for a track.
 type Major struct {
-	ID          string `json:"id"`
+	ID          JSONID `json:"id"`
 	Name        string `json:"name"`
 	Description string `json:"description"`
 }
 
 // TrackLyricsInfo represents minimal lyrics info for a track.
 type TrackLyricsInfo struct {
-	ID        string `json:"id"`
+	ID        JSONID `json:"id"`
 	Text      string `json:"text"`
 	Major     *Major `json:"major"`
 	Available bool   `json:"available"`