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/models/label.go

@@ -1,10 +1,11 @@
+// Package models provides data models for the Yandex Music API.
 package models
 
 import (
 	"encoding/json"
 )
 
-// Label represents a label
+// Label represents a label from the Yandex Music API.
 type Label struct {
 	BaseModel
 	ID          string       `json:"id"`
@@ -17,7 +18,7 @@ type Label struct {
 	Owner       *User        `json:"owner"`
 }
 
-// DeJSON deserializes a Label from JSON
+// DeJSON deserializes a Label from JSON data.
 func (l *Label) DeJSON(data []byte, client ClientInterface) (Model, error) {
 	var raw map[string]json.RawMessage
 	if err := json.Unmarshal(data, &raw); err != nil {
@@ -58,7 +59,7 @@ func (l *Label) DeJSON(data []byte, client ClientInterface) (Model, error) {
 	return label, nil
 }
 
-// DeList deserializes a list of Labels
+// DeList deserializes a list of Labels from JSON data.
 func (l *Label) DeList(data []byte, client ClientInterface) ([]Model, error) {
 	var rawList []json.RawMessage
 	if err := json.Unmarshal(data, &rawList); err != nil {
@@ -76,7 +77,7 @@ func (l *Label) DeList(data []byte, client ClientInterface) ([]Model, error) {
 	return result, nil
 }
 
-// LabelAlbums represents label albums
+// LabelAlbums represents label albums.
 type LabelAlbums struct {
 	BaseModel
 	Albums   []Album `json:"albums"`
@@ -85,7 +86,7 @@ type LabelAlbums struct {
 	PageSize int     `json:"page_size"`
 }
 
-// LabelArtists represents label artists
+// LabelArtists represents label artists.
 type LabelArtists struct {
 	BaseModel
 	Artists  []Artist `json:"artists"`