Implement new package with multichain demo frontend app

[esaminu]

Description

• [ ] Deploy to vercel
• [ ] Hardcode an account with a FAK locally first to get it working with signMultichain then in future use fastauth sign in and create account
• [ ] Once signed in, use multichain account id value from config (possibly env) to fetch the root key and derive accounts for in canonical JSON per https://github.com/near/near-fastauth-wallet/blob/dmd/chain_sig_docs/docs/chain_signature_api.org#serialization-format: - {"chain": 0, "domain": "near.org"} - {"chain": 0} - {"chain": 60, "domain": "near.org"} - {"chain": 60}
• [ ] Allow users to select the type of key from a dropdown in the detail page
• [ ] Implement second route for the detail with an amount and "Send" button which calls near-fastauth-wallet signMultichain method https://github.com/near/near-fastauth-wallet/issues/17