FIP: ENS Support in Hubs

Farcaster's FIP "ENS Usernames" proposes a two-tier naming system in which users choose between a free off-chain ENS name (fname) moderated by the Farcaster team or a decentralized on-chain ENS name that costs gas. Fnames are issued under the fcast.id ENS namespace via CCIP by a nameserver at fnames.facaster.xyz, and users can claim one by submitting an EIP-712 signed message proving ownership of an fid. Hubs will track valid usernames, re-validate ownership, and emit events when usernames change, and a validation job runs at 2am UTC to revoke USER_DATA.USERNAME messages that are no longer correctly owned.