We want to be able to specify Farcaster users based on FIDs in EntityText, so that we can resolve them to their usernames in robotext and notifs.

Depends on D11878

I tested this in combination with later diffs on both keyserver and web:

1. For keyserver, I tested that Farcaster usernames worked in notifs
2. For web, I tested that Farcaster usernames were resolved in robotext