Server-agnostic hostnames

I'd propose allowing each user a <username>.usbx.me domain that stays consistent across migrations. This would have the benefit of reducing friction during upgrades and making things easier on less-tech-literate users of our services, as well as circumventing the most frequently-cited issue with custom domains -- liability and dissociation from the Ultra.cc brand. If this is possible within the networking constraints of the system, I think it could be a lovely QOL improvement.

Context: in a recent migration I had to update probably 15 different integrations with the new URL, and still haven't gotten around to contacting friends to let them know their URLs have changed. Let's make this easier on our users (and sub-users) in the future! :-)