Deletes up to 1000 anonymous users by email, along with all of their stored preferences. Does not affect SSO (non-anonymous) accounts.

Body: a JSON array of email strings.

Response: 200 OK with an array of { email, error } entries for rows that failed (invalid email format, internal error). Emails that did not match any anonymous user are silently skipped (not an error). An empty array means every email either deleted cleanly or did not exist.