test: add isolated production acceptance harness

package.json

@@ -18,6 +18,7 @@
     "dist:mac": "electron-builder --mac dmg && node scripts/prune-dist.mjs",
     "doctor": "node scripts/doctor.mjs",
     "acceptance": "node scripts/acceptance.mjs",
+    "acceptance:isolated": "node --test tests/production-acceptance.test.mjs",
     "architecture:audit": "node scripts/architecture-audit.mjs",
     "test:browser": "playwright test",
     "test:browser:ci": "playwright test --reporter=line,html",