refactor: consolidate download domain into download package

internal/download/options.go

@@ -0,0 +1,38 @@
+package download
+
+import (
+	"fmt"
+	"time"
+)
+
+var validQualities = map[string]bool{
+	"mp3_128": true,
+	"mp3_320": true,
+	"flac":    true,
+}
+
+type Options struct {
+	Quality string
+	Timeout time.Duration
+	Limit   int
+	BPM     bool
+	Genre   bool
+	Strict  bool
+}
+
+func (o *Options) Validate() error {
+	if !validQualities[o.Quality] {
+		return fmt.Errorf("invalid quality option: %s", o.Quality)
+	}
+	if o.Timeout <= 0 {
+		return fmt.Errorf("timeout must be a positive duration")
+	}
+	if o.Limit <= 0 {
+		return fmt.Errorf("limit must be a positive integer")
+	}
+	if o.Limit > 100 {
+		return fmt.Errorf("limit must not exceed 100")
+	}
+
+	return nil
+}