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/handler/keyboard.go

@@ -80,6 +80,22 @@ func progressKeyboard(pct float64, speed, eta string) models.InlineKeyboardMarku
 	}
 }
 
+// mediaTypeKeyboard builds the initial type picker (Video/Audio/Ask).
+func mediaTypeKeyboard() models.InlineKeyboardMarkup {
+	return models.InlineKeyboardMarkup{
+		InlineKeyboard: [][]models.InlineKeyboardButton{
+			{
+				{Text: "Video", CallbackData: "type_video"},
+				{Text: "Audio", CallbackData: "type_audio"},
+				{Text: "Ask", CallbackData: "type_ask"},
+			},
+			{
+				{Text: "Cancel", CallbackData: "cancel_dl"},
+			},
+		},
+	}
+}
+
 // deleteConfirmKeyboard builds the confirmation prompt for account deletion.
 func deleteConfirmKeyboard(userID int64) models.InlineKeyboardMarkup {
 	return models.InlineKeyboardMarkup{