Add backend CORS configuration documentation

[godekina]

Add backend CORS configuration documentation

Repository: PolymorphicAI/study-copilot

Suggested Labels: documentation, backend, security, trivial, wave-ready

Suggested Complexity: Trivial / 100 points

---

Summary

Document CORS configuration for local and future deployment.

Why This Matters

Frontend-backend connection issues often come from CORS misconfiguration.

Tasks

• Review current CORS setup if any.
• Document local development settings.
• Document safer production recommendations.
• Add troubleshooting notes.

Acceptance Criteria

• CORS documentation exists.
• Local and production notes are included.
• Troubleshooting is included.

Suggested Complexity

Trivial / 100 points

Suggested Labels

documentation, backend, security, trivial, wave-ready