Enable runtime Supabase configuration and UX polish

[Alecbdc]

Summary

• add localStorage-backed Supabase override helpers plus an auth-screen backend panel so the app can switch between demo and real Supabase projects at runtime
• tighten the curriculum experience with a visible passing-score hint, improved quiz logging, and completion button states tied to progress
• document the runtime backend workflow so reviewers can make the platform fully operational without editing source files

Testing

• python3 -m http.server 4173 & curl -I http://localhost:4173/

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Codex Task