Re-apply the deeplink backend deferred out of PR1a: migration 00006 adds
email_confirmations.purpose + link_token_hash (hand-edited jet), each issued code
now carries an opaque 256-bit token (only its SHA-256 stored), and ConfirmByToken
resolves a token to a login (confirm + clear guest) or a link (attach when free,
signal merge when owned elsewhere). issueCode now embeds the /app/#/confirm/<token>
link in the email. The confirm endpoint, gateway RPC and SPA route follow.
Ilia Denisov