Unauthenticated reading of every file via livechat auth and predicting MongoDB ObjectId()

Summary

Protected file downloads at /file-upload/:fileId/:name authorize livechat access using rc_room_type=l with rc_rid+rc_token, but the authorization path does not verify that rc_rid matches the requested file's rid. Furthermore, :fileId is predictable via sequential MongoDB IDs, and :name can be anything, allowing unauthenticated discovery of all uploaded files.