Update runtime ports and deployment defaults.

Switch backend/frontend to ports 8074/8075 and align Docker, CORS, frontend API base URL, and docs so deployment uses the new endpoints consistently.

backend/.env.example

@@ -9,7 +9,7 @@ API_KEY=change-me-in-production-min-16-chars
 DATABASE_URL=postgresql+psycopg://genexamenes:genexamenes@db:5432/genexamenes
 
 # --- CORS (orígenes del frontend, separados por coma) ---
-ALLOWED_ORIGINS=http://localhost:5173,http://localhost:3000
+ALLOWED_ORIGINS=http://localhost:8075
 
 # --- Rate limiting y tamaño de petición ---
 RATE_LIMIT_REQUESTS=60