Unify information exposed via user domain and profile.

[RokeJulianLockhart]

As https://forum.newsblur.com/t/how-to-link-to-newsblur-profile-with-uri/10207/2?u=rokejulianlockhart explains, both

and https://rokejulianlockhart.newsblur.com/ exist. However, the profile displays more useful information. This is problematic, because I'd like a URI to this information so that others can view it.

A potential solution is #1859 (comment), but I'd prefer to have the "profile" merely display an <iframe> of the subdomain, properly styled and displaying the same information.