ci: re-enable Lighthouse workflow when multei.com.br is back online

Context

The Lighthouse GitHub Actions workflow audits https://multei.com.br on every push. Production currently fails LHCI collect with CHROME_INTERSTITIAL_ERROR (Chrome interstitial / site unavailable), so the workflow was temporarily disabled (trigger changed from push to workflow_dispatch only).

Related:

• Toolchain fix: #418
• Example failing collect after Action upgrades: https://github.com/multei/web/actions/runs/29500972827

Goal

Re-enable automatic Lighthouse runs on push once https://multei.com.br loads cleanly without a Chrome interstitial.

Suggested scope

• Confirm https://multei.com.br responds successfully in a clean browser (no SSL/DNS/interstitial warning).
• In .github/workflows/lighthouse.yml, restore on: [push] (keep workflow_dispatch optional if useful).
• Remove or update the temporary-disable comments in that file.
• Trigger a workflow run and confirm LHCI collect + artifact upload succeed.
• Clear or update the related notes in TROUBLESHOOTING.md if the interstitial issue is resolved.

Acceptance criteria

• Lighthouse workflow runs automatically on push again.
• A recent run is green (or fails only on real Lighthouse score/assertions, not interstitial/toolchain).
• lighthouseresults artifact is published.

Notes

• Do not re-enable on push while the production URL still shows an interstitial or is otherwise unreachable to Chrome.

First check https://multei.com.br in a clean browser and review the failing collect run linked in the issue. Then inspect .github/workflows/lighthouse.yml and the related notes in TROUBLESHOOTING.md. Done means push-triggered Lighthouse runs are restored, a recent run completes without an interstitial failure, and the lighthouseresults artifact is published.