Feat/backend api integration

[nasseralkawari]

This PR completes the frontend-to-backend quiz flow integration and fixes the related configuration issues discovered during testing.

Changes included:

• updated quiz generation request to use the correct backend route

  • POST /api/quiz/generate

• updated quiz submission request to use the correct backend route

  • POST /api/quiz/submit

• connected GenerateQuizPage to the real backend instead of mock quiz data

• connected QuizPage to backend scoring and result submission

• updated FeedbackPage to display backend-driven score and result data

• fixed backend development setup so API routes can be tested without requiring the frontend production build

• identified and resolved missing GEMINI_API_KEY environment configuration

• validated backend health route and request flow during integration testing

Why this PR:

• enables real quiz generation from the backend
• enables real quiz submission and scoring
• improves full-stack integration quality
• resolves development-time configuration blockers

Notes:

• backend must have valid environment variables configured, especially GEMINI_API_KEY
• frontend and backend should be run in separate terminals during development
• API health endpoint used for verification: /api/quiz/health

This PR focuses on backend integration, request routing, scoring flow, and environment/configuration fixes needed to make the application work end-to-end.