fix: show bitrate for audio-only formats, filter subtitle languages, improve feedback

- Prioritize IsAudioOnly check in formatLabelForDisplay so bitrate
  is shown instead of yt-dlp's generic 'audio only' resolution
- Only collect languages from formats with audio/video to prevent
  subtitle-only tracks from triggering the language selection prompt
- Show 'Fetching metadata...' message before GetMediaInfo and edit
  with results, improving UX for URL input
- Add test coverage for audio-only format labels

internal/dl/ytdlp.go

@@ -171,7 +171,9 @@ func (c *Client) GetMediaInfo(url string) (*domain.MediaInfo, error) {
 	for _, f := range info.Formats {
 		ff := c.convertFormat(f)
 		mi.Formats = append(mi.Formats, ff)
-		if ff.Language != "" && !langSet[ff.Language] {
+		// Only consider languages from formats with audio or video to avoid
+		// prompting for subtitle-only or auto-generated caption languages.
+		if (ff.HasAudio || ff.HasVideo) && ff.Language != "" && !langSet[ff.Language] {
 			langSet[ff.Language] = true
 			mi.Languages = append(mi.Languages, ff.Language)
 		}