Change the instance's settings

Matches the email to a person: an existing member just gets the grants, all or none (200); anyone else is `invited` until they accept (201), a removed member and a person with an account included. By email, an account with a password and a verified email gets a notice to sign in and accept, with a link to Studio's `/accept-invite` and no code; anyone else (a new person, whose account is made now, or one whose account has no password or an unverified email) gets an invite code. A person whose own sign-up is pending is 409 `signup_pending`: approve it instead. With `delivery: "link"` (only for a new person, or an account with no password and an unverified email that no other tenant holds by an invite or a membership; else 409 `link_not_allowed`, send by email) nothing is mailed (no SMTP needed): the response carries the link with its code as `invite_url`, once, with `Cache-Control: no-store`; it is never stored or logged. Invite mails and codes are limited to 5 per person per hour, resends included (429 `rate_limited`). Every grant is checked first, as `putProjectGrant` checks it, with the member's overrides.