Add a Lighthouse CI performance budget to the CI workflow

[anurag629]

Context

Part of the SEO growth initiative (#18): Phase 4: Compound and technical polish.
A performance budget in CI keeps Core Web Vitals from regressing as the site grows, protecting rankings and clicks.

What to do

• Add Lighthouse CI (or an equivalent) to the CI workflow with budgets for LCP, CLS, and total bundle.
• Fail or warn the PR when a budget is exceeded.

Where

.github/workflows/ci.yml; align with the existing lint/test/build jobs.

Acceptance criteria

• Lighthouse budget runs in CI and reports on PRs
• npm run lint && npm run test && npm run build passes

Notes

Branch off develop (feat/*, docs/*, chore/*), open a PR into develop, and squash-merge. See CONTRIBUTING.md.