Adapt CI/CD and endpoint defaults for Sinbad2 production.

Configure GitLab deploy pipeline for this app and switch backend/frontend endpoint defaults from localhost to sinbad2.ujaen.es, including Docker, env files, API client, CORS, and docs.

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:8075
+ALLOWED_ORIGINS=http://sinbad2.ujaen.es,http://sinbad2.ujaen.es:8075
 
 # --- Rate limiting y tamaño de petición ---
 RATE_LIMIT_REQUESTS=60