Add server security hardening and draft quiz persistence

Security:
- Add AES-256-GCM encryption for user PII (email, API keys, config)
- Add rate limiting (helmet + express-rate-limit)
- Require auth for file uploads

UX:
- Persist draft quizzes to sessionStorage (survives refresh)
- Add URL-based edit routes (/edit/draft, /edit/:quizId)
- Fix QuizEditor async defaultConfig race condition
- Fix URL param accumulation in Landing

.env.example

@@ -3,6 +3,7 @@
 # ==============================================================================
 PG_PASS=
 AUTHENTIK_SECRET_KEY=
+ENCRYPTION_KEY=
 
 # ==============================================================================
 # HOST CONFIGURATION