ci(bstein-home): stabilize playwright e2e server

Jenkinsfile

@@ -300,6 +300,7 @@ PY
           sh(script: '''#!/usr/bin/env bash
 set -euo pipefail
 mkdir -p build
+ulimit -n 8192 || true
 cd frontend
 set +e
 npm_ci_rc=1

testing/frontend/playwright.config.mjs

@@ -13,7 +13,7 @@ export default defineConfig({
     viewport: { width: 1440, height: 1080 },
   },
   webServer: {
-    command: "npm run dev -- --host 127.0.0.1 --port 4173",
+    command: "npm run build && npm run preview -- --host 127.0.0.1 --port 4173",
     cwd: frontendRoot,
     url: "http://127.0.0.1:4173",
     reuseExistingServer: !process.env.CI,