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/labels.go

@@ -1,3 +1,4 @@
+// Package client provides methods for interacting with Yandex Music API endpoints.
 package client
 
 import (
@@ -7,7 +8,7 @@ import (
 	"gitea.mrixs.me/Mrixs/yandex-music-api-go/internal/models"
 )
 
-// GetLabels gets all labels
+// GetLabels gets all labels (GET /labels).
 func (c *Client) GetLabels(ctx context.Context) ([]*models.Label, error) {
 	var result []models.Label
 	if err := c.request.Get(ctx, "/labels", nil, &result); err != nil {
@@ -22,8 +23,7 @@ func (c *Client) GetLabels(ctx context.Context) ([]*models.Label, error) {
 	return labels, nil
 }
 
-// GetLabel gets a label by ID
-// GET /labels/{labelID}
+// GetLabel gets a label by ID (GET /labels/{labelID}).
 func (c *Client) GetLabel(ctx context.Context, labelID string) (*models.Label, error) {
 	var result models.Label
 	if err := c.request.Get(ctx, fmt.Sprintf("/labels/%s", labelID), nil, &result); err != nil {
@@ -33,8 +33,7 @@ func (c *Client) GetLabel(ctx context.Context, labelID string) (*models.Label, e
 	return &result, nil
 }
 
-// GetLabelAlbums gets albums for a label
-// GET /labels/{labelID}/albums
+// GetLabelAlbums gets albums for a label (GET /labels/{labelID}/albums).
 func (c *Client) GetLabelAlbums(ctx context.Context, labelID string, page, pageSize int) (*models.LabelAlbums, error) {
 	params := map[string]string{}
 	if page > 0 {
@@ -51,8 +50,7 @@ func (c *Client) GetLabelAlbums(ctx context.Context, labelID string, page, pageS
 	return &result, nil
 }
 
-// GetLabelArtists gets artists for a label
-// GET /labels/{labelID}/artists
+// GetLabelArtists gets artists for a label (GET /labels/{labelID}/artists).
 func (c *Client) GetLabelArtists(ctx context.Context, labelID string, page, pageSize int) (*models.LabelArtists, error) {
 	params := map[string]string{}
 	if page > 0 {