refactor(media): centralize temp media dir path

pkg/utils/media.go

@@ -12,6 +12,7 @@ import (
 	"github.com/google/uuid"
 
 	"github.com/sipeed/picoclaw/pkg/logger"
+	"github.com/sipeed/picoclaw/pkg/media"
 )
 
 // IsAudioFile checks if a file is an audio file based on its filename extension and content type.
@@ -67,7 +68,7 @@ func DownloadFile(urlStr, filename string, opts DownloadOptions) string {
 		opts.LoggerPrefix = "utils"
 	}
 
-	mediaDir := filepath.Join(os.TempDir(), "picoclaw_media")
+	mediaDir := media.TempDir()
 	if err := os.MkdirAll(mediaDir, 0o700); err != nil {
 		logger.ErrorCF(opts.LoggerPrefix, "Failed to create media directory", map[string]any{
 			"error": err.Error(),