Add package-level godoc documentation

- models: Package doc comment describing data models with DeJSON/DeList
- utils: Package doc comment for utility functions (JSON, signing, schema mismatch, errors)
- ynison: Package doc comment for Ynison WebSocket client protocol

Co-Authored-By: Claude Code <noreply@anthropic.com>

internal/models/base.go

@@ -1,3 +1,5 @@
+// Package models provides data models for the Yandex Music API.
+// All models implement the Model interface with DeJSON/DeList deserialization methods.
 package models
 
 import (

internal/utils/schema.go

@@ -1,3 +1,5 @@
+// Package utils provides utility functions for the Yandex Music API client,
+// including JSON handling, request signing, schema mismatch tracking, and error types.
 package utils
 
 import (

internal/ynison/client.go

@@ -1,3 +1,5 @@
+// Package ynison provides a WebSocket client for the Yandex Music Ynison protocol,
+// enabling real-time player synchronization across devices.
 package ynison
 
 import (