feat: add auto-select from preferences and type picker

- Add MediaTypeAsk (0) as the default, mapping old video_audio to Ask
- Show Video/Audio/Ask type picker when no default media type is set
- Auto-select matching format and skip picker when defaults are configured
- Add autoSelectVideoFormat / autoSelectAudioFormat helpers with closest-match
- Add buildFilteredFormatList for type-filtered format lists
- Add Media Type setting in settings UI (Ask/Video/Audio)
- Add --merge-output-format mp4 for video downloads via yt-dlp
- Fix formatLabelForDisplay to show Height fallback and Extension
- Add cookies volume mount to docker-compose.yml
- Document cookies setup and new features in README

internal/repo/store.go

@@ -65,7 +65,7 @@ func (s *Store) GetOrCreateUser(chatID int64) (int64, error) {
 
 func (s *Store) GetOrCreatePreferences(userID int64) (*domain.UserPreferences, error) {
 	if _, err := s.db.Exec(
-		"INSERT OR IGNORE INTO user_preferences (user_id) VALUES (?)",
+		"INSERT OR IGNORE INTO user_preferences (user_id, default_media_type) VALUES (?, 'ask')",
 		userID,
 	); err != nil {
 		return nil, err
@@ -90,14 +90,18 @@ func (s *Store) getPreferences(userID int64) (*domain.UserPreferences, error) {
 		p.DefaultMediaType = domain.MediaTypeAudio
 	case "video":
 		p.DefaultMediaType = domain.MediaTypeVideo
+	case "ask":
+		p.DefaultMediaType = domain.MediaTypeAsk
 	default:
-		p.DefaultMediaType = domain.MediaTypeVideoAudio
+		p.DefaultMediaType = domain.MediaTypeAsk
 	}
 	return &p, nil
 }
 
 func mediaTypeToString(mt domain.MediaType) string {
 	switch mt {
+	case domain.MediaTypeAsk:
+		return "ask"
 	case domain.MediaTypeAudio:
 		return "audio"
 	case domain.MediaTypeVideo: