error.tsx: stale-server-action hard-reload recovery

Root error boundary (src/app/error.tsx) 'Reintentar'=reset() is a soft re-render that keeps the stale pre-deploy bundle, so for the Next.js stale-server-action-after-redeploy class it can re-error; only 'Volver al inicio' recovers. Detect the stale-action signature (errorMessage ~ 'was not found on the server') and hard-reload (window.location.reload()) instead of soft reset() so the intuitive button fetches the fresh bundle. Guard against reload-loop (once-only flag). ~5 lines, single-file, reversible. Origin: applog b1b9f590 benign-close (deploy-churn one-off), coder proposed hardening.