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/artist_albums.go

@@ -1,17 +1,18 @@
+// Package models provides data models for the Yandex Music API.
 package models
 
 import (
 	"encoding/json"
 )
 
-// ArtistAlbums represents a page of albums by an artist
+// ArtistAlbums represents a page of albums by an artist.
 type ArtistAlbums struct {
 	BaseModel
 	Albums []Album `json:"albums"`
 	Pager  *Pager  `json:"pager"`
 }
 
-// DeJSON deserializes an ArtistAlbums from JSON
+// DeJSON deserializes an ArtistAlbums from JSON data.
 func (aa *ArtistAlbums) DeJSON(data []byte, c ClientInterface) (Model, error) {
 	var raw map[string]json.RawMessage
 	if err := json.Unmarshal(data, &raw); err != nil {
@@ -36,7 +37,7 @@ func (aa *ArtistAlbums) DeJSON(data []byte, c ClientInterface) (Model, error) {
 	return albums, nil
 }
 
-// DeList deserializes a list of ArtistAlbums
+// DeList deserializes a list of ArtistAlbums from JSON data.
 func (aa *ArtistAlbums) DeList(data []byte, c ClientInterface) ([]Model, error) {
 	var rawList []json.RawMessage
 	if err := json.Unmarshal(data, &rawList); err != nil {