Add comprehensive godoc documentation to all exported symbols

- Document all exported types, functions, methods, and constants across 52 files
- Add package-level doc comments to client, models, utils, and ynison packages
- Document HTTP method and endpoint path for each API client method
- Document model struct fields and DeJSON/DeList/ToJSON/ToMap methods
- Fix duplicate package doc comment in internal/models/base.go

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

internal/client/supplements.go

@@ -1,3 +1,4 @@
+// Package client provides methods for interacting with Yandex Music API endpoints.
 package client
 
 import (
@@ -9,8 +10,7 @@ import (
 	"gitea.mrixs.me/Mrixs/yandex-music-api-go/internal/utils"
 )
 
-// GetTrackSupplement gets supplement for a track
-// GET /tracks/{track_id}/supplement
+// GetTrackSupplement gets supplement for a track (GET /tracks/{track_id}/supplement).
 func (c *Client) GetTrackSupplement(ctx context.Context, trackID string) (*models.Supplement, error) {
 	path := fmt.Sprintf("/tracks/%s/supplement", trackID)
 
@@ -21,8 +21,9 @@ func (c *Client) GetTrackSupplement(ctx context.Context, trackID string) (*model
 	return &result, nil
 }
 
-// GetTrackLyrics gets lyrics for a track (new endpoint with signing)
-// GET /tracks/{track_id}/lyrics
+// GetTrackLyrics gets lyrics for a track (GET /tracks/{track_id}/lyrics).
+// The format parameter specifies the lyrics format (e.g., "TEXT" or "LRC").
+// The request is signed using the default signing key.
 func (c *Client) GetTrackLyrics(ctx context.Context, trackID string, format string) (*models.TrackLyrics, error) {
 	path := fmt.Sprintf("/tracks/%s/lyrics", trackID)
 
@@ -42,7 +43,7 @@ func (c *Client) GetTrackLyrics(ctx context.Context, trackID string, format stri
 	return &result, nil
 }
 
-// GetTrackLyricsText fetches the full lyrics text from the download URL
+// GetTrackLyricsText fetches the full lyrics text from the download URL provided in TrackLyrics.
 func (c *Client) GetTrackLyricsText(ctx context.Context, trackLyrics *models.TrackLyrics) (string, error) {
 	data, err := c.request.Download(ctx, trackLyrics.DownloadURL)
 	if err != nil {
@@ -51,8 +52,7 @@ func (c *Client) GetTrackLyricsText(ctx context.Context, trackLyrics *models.Tra
 	return string(data), nil
 }
 
-// GetLyrics gets lyrics info for a track (legacy endpoint)
-// GET /tracks/lyrics?track_id={track_id}
+// GetLyrics gets lyrics info for a track using the legacy endpoint (GET /tracks/lyrics).
 func (c *Client) GetLyrics(ctx context.Context, trackID string) (*models.LyricsInfo, error) {
 	params := map[string]string{
 		"track_id": trackID,
@@ -65,8 +65,7 @@ func (c *Client) GetLyrics(ctx context.Context, trackID string) (*models.LyricsI
 	return &result, nil
 }
 
-// GetVideoSupplement gets video supplement for a track (legacy endpoint)
-// GET /tracks/video-supplement?track_id={track_id}
+// GetVideoSupplement gets video supplement for a track using the legacy endpoint (GET /tracks/video-supplement).
 func (c *Client) GetVideoSupplement(ctx context.Context, trackID string) (*models.VideoSupplement, error) {
 	params := map[string]string{
 		"track_id": trackID,
@@ -79,44 +78,43 @@ func (c *Client) GetVideoSupplement(ctx context.Context, trackID string) (*model
 	return &result, nil
 }
 
-// GetLyricsByTrackID is an alias for GetTrackLyrics for backward compatibility
-// GET /tracks/{track_id}/lyrics
+// GetLyricsByTrackID is an alias for GetTrackLyrics for backward compatibility (GET /tracks/{track_id}/lyrics).
 func (c *Client) GetLyricsByTrackID(ctx context.Context, trackID string, format string) (*models.TrackLyrics, error) {
 	return c.GetTrackLyrics(ctx, trackID, format)
 }
 
-// LyricsFormat represents the lyrics format
+// LyricsFormat represents the lyrics format.
 type LyricsFormat string
 
 const (
-	// LyricsFormatText is plain text format
+	// LyricsFormatText is plain text lyrics format.
 	LyricsFormatText LyricsFormat = "TEXT"
-	// LyricsFormatLRC is LRC format with timestamps
+	// LyricsFormatLRC is LRC format lyrics with timestamps.
 	LyricsFormatLRC LyricsFormat = "LRC"
 )
 
-// GetTrackLyricsWithOptions gets lyrics with options
+// GetTrackLyricsWithOptions gets lyrics with options using a LyricsFormat value.
 func (c *Client) GetTrackLyricsWithOptions(ctx context.Context, trackID string, format LyricsFormat) (*models.TrackLyrics, error) {
 	return c.GetTrackLyrics(ctx, trackID, string(format))
 }
 
-// SupplementOptions holds options for supplement requests
+// SupplementOptions holds options for supplement requests.
 type SupplementOptions struct {
 	TrackID string
 }
 
-// GetSupplement gets track supplement with options
+// GetSupplement gets track supplement with options.
 func (c *Client) GetSupplement(ctx context.Context, opts SupplementOptions) (*models.Supplement, error) {
 	return c.GetTrackSupplement(ctx, opts.TrackID)
 }
 
-// LyricsOptions holds options for lyrics requests
+// LyricsOptions holds options for lyrics requests.
 type LyricsOptions struct {
 	TrackID string
 	Format  LyricsFormat
 }
 
-// GetLyricsWithOptions gets track lyrics with options
+// GetLyricsWithOptions gets track lyrics with options.
 func (c *Client) GetLyricsWithOptions(ctx context.Context, opts LyricsOptions) (*models.TrackLyrics, error) {
 	format := string(opts.Format)
 	if format == "" {
@@ -125,13 +123,14 @@ func (c *Client) GetLyricsWithOptions(ctx context.Context, opts LyricsOptions) (
 	return c.GetTrackLyrics(ctx, opts.TrackID, format)
 }
 
-// Sign represents a request signature
+// Sign represents a request signature for signed API requests.
 type Sign struct {
 	Timestamp int64
 	Value     string
 }
 
-// GetSignRequest creates a signature for a track request (exported for external use)
+// GetSignRequest creates a signature for a track request (exported for external use).
+// It delegates to utils.GetSignRequest with the default signing key.
 func GetSignRequest(trackID string) Sign {
 	h := utils.GetSignRequest(trackID, utils.DefaultSignKey)