Sign-in needs a Supabase project. Set it up once:

1. Create a new project at supabase.com/dashboard.
2. Authentication → Sign In / Providers: keep Email on and turn off Allow new users to sign up.
3. Authentication → Users → Add user: your email and password, with Auto Confirm User on.
4. Project Settings → API: copy the Project URL and the anon / publishable key.
5. Paste both into js/config.js and reload this page.