Non-members who register for an event now get a persistent identity:
with consent, a status:"guest" Member is upserted and an auth cookie is
set so the "You're Registered" state survives a page refresh.
Tiered auto-login matches passwordless-auth norms — auto-login is only
safe when the account holds no privileges:
- New email → create guest + cookie
- Returning guest → cookie
- Existing non-guest (active/pending/etc.) → attach ticket only, no
cookie, confirmation email includes a sign-in link
Guests are gated on status === "guest", so admin/middleware code that
keys on status === "active" naturally excludes them. Guests are also
treated as non-members for ticket pricing/validation to prevent picking
up member-only pricing on their second registration.