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/search.go

@@ -1,6 +1,7 @@
+// Package models provides data models for the Yandex Music API.
 package models
 
-// SearchResult represents search results
+// SearchResult represents search results from the Yandex Music API.
 type SearchResult struct {
 	Tracks    *SearchTracksResult    `json:"tracks"`
 	Albums    *SearchAlbumsResult    `json:"albums"`
@@ -10,43 +11,43 @@ type SearchResult struct {
 	Users     *SearchUsersResult     `json:"users"`
 }
 
-// SearchTracksResult represents track search results
+// SearchTracksResult represents track search results.
 type SearchTracksResult struct {
 	Total   int     `json:"total"`
 	Results []Track `json:"results"`
 }
 
-// SearchAlbumsResult represents album search results
+// SearchAlbumsResult represents album search results.
 type SearchAlbumsResult struct {
 	Total   int     `json:"total"`
 	Results []Album `json:"results"`
 }
 
-// SearchArtistsResult represents artist search results
+// SearchArtistsResult represents artist search results.
 type SearchArtistsResult struct {
 	Total   int      `json:"total"`
 	Results []Artist `json:"results"`
 }
 
-// SearchPlaylistsResult represents playlist search results
+// SearchPlaylistsResult represents playlist search results.
 type SearchPlaylistsResult struct {
 	Total   int        `json:"total"`
 	Results []Playlist `json:"results"`
 }
 
-// SearchVideosResult represents video search results
+// SearchVideosResult represents video search results.
 type SearchVideosResult struct {
 	Total   int     `json:"total"`
 	Results []Video `json:"results"`
 }
 
-// SearchUsersResult represents user search results
+// SearchUsersResult represents user search results.
 type SearchUsersResult struct {
 	Total   int    `json:"total"`
 	Results []User `json:"results"`
 }
 
-// SearchBanner represents a search banner
+// SearchBanner represents a search banner.
 type SearchBanner struct {
 	ID          string `json:"id"`
 	Title       string `json:"title"`
@@ -57,7 +58,7 @@ type SearchBanner struct {
 	Type        string `json:"type"`
 }
 
-// Tag represents a search tag
+// Tag represents a search tag.
 type Tag struct {
 	ID          string `json:"id"`
 	Title       string `json:"title"`
@@ -66,7 +67,7 @@ type Tag struct {
 	Type        string `json:"type"`
 }
 
-// Video represents a video (minimal)
+// Video represents a video (minimal).
 type Video struct {
 	BaseModel
 	ID         string `json:"id"`