Initial commit: ym-dl with yandex-music-api-go library migration

Migrate ym-dl from custom oapi-codegen Yandex Music API client to external
gitea.mrixs.me/Mrixs/yandex-music-api-go library with token-only authentication.

Key changes:
- Replace custom Yandex API client with yandexmusic library wrapper
- Token-based OAuth authentication only (no username/password fallback)
- SQLite storage index with JSON index migration path
- Extended ID3 tag support: genre, comment, lyrics, publisher, ISRC, copyright
- High-resolution album covers (1000x1000)
- Fixed album download check (requires all tracks, not just one)

internal/config/config.go

@@ -0,0 +1,92 @@
+package config
+
+import (
+	"errors"
+	"os"
+	"time"
+
+	"gopkg.in/yaml.v3"
+)
+
+// Config holds the application configuration
+type Config struct {
+	Yandex  YandexConfig  `yaml:"yandex"`
+	Artists []Artist      `yaml:"artists"`
+	Storage StorageConfig `yaml:"storage"`
+	Monitor MonitorConfig `yaml:"monitor"`
+	Debug   bool          `yaml:"debug"`
+}
+
+// YandexConfig holds Yandex Music API credentials
+type YandexConfig struct {
+	Token    string `yaml:"token"`
+	Username string `yaml:"username"`
+	Password string `yaml:"password"`
+}
+
+// Artist represents an artist to monitor
+type Artist struct {
+	ID int `yaml:"id"`
+}
+
+// StorageConfig holds storage settings
+type StorageConfig struct {
+	Path     string `yaml:"path"`
+	Organize bool   `yaml:"organize"`
+}
+
+// MonitorConfig holds monitor settings
+type MonitorConfig struct {
+	Interval string `yaml:"interval"`
+}
+
+// Load loads configuration from a YAML file
+func Load(path string) (*Config, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	var cfg Config
+	if err := yaml.Unmarshal(data, &cfg); err != nil {
+		return nil, err
+	}
+
+	if err := cfg.Validate(); err != nil {
+		return nil, err
+	}
+
+	return &cfg, nil
+}
+
+// Validate validates the configuration
+func (c *Config) Validate() error {
+	if len(c.Artists) == 0 {
+		return errors.New("at least one artist must be configured")
+	}
+
+	for _, a := range c.Artists {
+		if a.ID <= 0 {
+			return errors.New("artist ID must be positive")
+		}
+	}
+
+	if c.Storage.Path == "" {
+		return errors.New("storage path is required")
+	}
+
+	if c.Yandex.Token == "" && (c.Yandex.Username == "" || c.Yandex.Password == "") {
+		return errors.New("either yandex.token or yandex.username/password must be provided")
+	}
+
+	if _, err := time.ParseDuration(c.Monitor.Interval); err != nil {
+		return errors.New("monitor.interval must be a valid duration (e.g., 24h, 1h, 7d)")
+	}
+
+	return nil
+}
+
+// GetMonitorInterval returns the parsed monitor interval
+func (c *Config) GetMonitorInterval() (time.Duration, error) {
+	return time.ParseDuration(c.Monitor.Interval)
+}