🤖 The Vault can now be **locked with a passkey**. A locked vault's values only
open after Touch ID / Face ID — on any device, in any browser where you've set up
your passkey. Anyone in the chat can still *add* a secret without unlocking, and
names and history stay visible; only reading a value asks for the biometric.
Sharing is just membership: add the Vault to a chat and everyone in it is in —
each person sets up their own passkey the first time, and anyone already in can
give a newcomer access, all without any secret leaving the encryption. Locking
is one-way, and as ever, the server only ever sees ciphertext.