feat(enterprise): verify D5 lease recovery

[Gracker]

Summary

• reload visible Perfetto UI pages when backend lease heartbeat reports a stale/unrecoverable lease
• add D5 to the enterprise window regression script: offline holder grace, stale-holder sweep, and pageshow-style same-lease reacquire
• mark §0.7 D5 complete and refresh prebuilt frontend to v54.0-a42c0bb58

Stack

• Base PR: feat(enterprise): heartbeat UI lease targets #101 (feature/enterprise-multi-tenant-ui-lease-heartbeat)
• Submodule commit: a42c0bb586 feat(ui): recover stale trace processor leases pushed to fork
• Root commit: 14deff1f feat(enterprise): verify D5 lease recovery

Verification

• cd backend && npx jest --runInBand --forceExit src/scripts/__tests__/verifyEnterpriseMultiTenantWindows.test.ts
• cd backend && npm run typecheck
• cd perfetto && node ui/build.js --no-wasm --run-unittests --test-filter="HttpRpcEngine"
• ./scripts/update-frontend.sh
• ./scripts/start-dev.sh --quick plus Playwright browser smoke check: browser-ok title="Perfetto UI" manifest=200
• npm run verify:pr