An invitation carries no password. The HQ password is what signs someone
into every instance they are granted, so a password the inviter chose would
be a shared credential to all of them — the invited row has an empty hash,
which cannot authenticate, until /accept-invite sets one.
Removing a person revokes every projected instance user first, and refuses
outright if any of those is an instance's last owner.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>