fix(telegram): defaultDocumentHandler MEDIA format — remove leaked filename

The format 'MEDIA:document:path:fileName' had 3 colon-separated parts,
but sendMedia only parses 2 (type:path). The fileName leaked into the
path, causing os.Stat to fail. Fixed to clean 'MEDIA:document:path'.
Telegram's sendDocument gets the filename from the file itself.

Author: molty3000

internal/telegram/handler.go

@@ -170,7 +170,7 @@ func defaultDocumentHandler(bot *Bot) func(int64, int, string, string) (string,
 		if err != nil {
 			return "", fmt.Errorf("telegram handler: download document: %w", err)
 		}
-		return fmt.Sprintf("MEDIA:document:%s:%s", path, fileName), nil
+		return fmt.Sprintf("MEDIA:document:%s", path), nil
 	}
 }