show NIP-05 address on profiles with npubs

e.g. nostroots@trustroots.org

Possibly with:
- hover to explain that this is not an email address
- suggestion to use https://www.0xchat.com/?
- if at all possible, a nostr messaging URL?
(Reusing `@` doesn't seem like the brightest idea at this point, but didn't dive into the rationale for this.)

Might as well fix #2693 while at it.