consider adding hostname to register delegation

[holic]

when we create an app signer, we tie the signed message to the hostname signing it to ensure one app signer per hostname

however, there's no way to retrieve this later on if we want to e.g. list all of your delegations, balances associated, and hostnames to recover the app signer to withdraw balance

not sure I love putting the hostname<>signer/account relationship onchain but services like relay already add metadata like this to the chain so maybe it's fine/not a huge security/privacy risk?

[holic]

if we only care about this in the context of account kit and if we plan to move account kit to a single hostname to serve iframes, we may not need to worry about this because the one hostname should have all of this in localstorage