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/history.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"
 )
 
-// GetMusicHistory gets music history
+// GetMusicHistory gets the user's music history (GET /music-history).
 func (c *Client) GetMusicHistory(ctx context.Context) (*models.MusicHistory, error) {
 	var result models.MusicHistory
 	if err := c.request.Get(ctx, "/music-history", nil, &result); err != nil {
@@ -16,7 +17,7 @@ func (c *Client) GetMusicHistory(ctx context.Context) (*models.MusicHistory, err
 	return &result, nil
 }
 
-// GetMusicHistoryTabs gets music history tabs
+// GetMusicHistoryTabs gets music history tabs (GET /music-history/tabs).
 func (c *Client) GetMusicHistoryTabs(ctx context.Context) ([]*models.MusicHistoryTab, error) {
 	var result []models.MusicHistoryTab
 	if err := c.request.Get(ctx, "/music-history/tabs", nil, &result); err != nil {
@@ -31,7 +32,7 @@ func (c *Client) GetMusicHistoryTabs(ctx context.Context) ([]*models.MusicHistor
 	return tabs, nil
 }
 
-// GetMusicHistoryItems gets music history items
+// GetMusicHistoryItems gets music history items for a tab (GET /music-history/items).
 func (c *Client) GetMusicHistoryItems(ctx context.Context, tabID string, page, pageSize int) (*models.MusicHistoryItems, error) {
 	params := map[string]string{}
 	if tabID != "" {