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/handler/handler_test.go

@@ -194,6 +194,18 @@ func TestFormatLabelForDisplay(t *testing.T) {
 			f:    domain.Format{ID: "137"},
 			want: "137",
 		},
+		{
+			f:    domain.Format{IsAudioOnly: true, Bitrate: "128k", Filesize: 1048576, Resolution: "audio only"},
+			want: "128k (1.0MB)",
+		},
+		{
+			f:    domain.Format{IsAudioOnly: true, Bitrate: "128k", Resolution: "audio only"},
+			want: "128k",
+		},
+		{
+			f:    domain.Format{IsAudioOnly: true, ID: "140", Extension: "m4a", Filesize: 1048576, Resolution: "audio only"},
+			want: "140 (m4a) (1.0MB)",
+		},
 	}
 	for _, tt := range tests {
 		got := formatLabelForDisplay(tt.f)