Sign in before beta checkout or beta access.
This uses Supabase email/password auth. The free Public Demo does not require sign-in; paid beta access should be tied to the same email used during checkout.
✓Real Supabase session handling, not a fake static password form.
✓Beta access is tied to your signed-in user and payment email.
✓Production payment-to-access uses Stripe payment confirmation and Supabase entitlement records.