tooling: Lighthouse CI budgets (perf / a11y / SEO / best-practices)

[VijitSingh97]

Part of the v1.1 site-tooling set · companion to #11.

This is a public, single-page showcase landing site, but there are no perf, accessibility, or SEO checks — regressions (oversized images, broken meta/OG tags, contrast/a11y issues, render-blocking assets) can ship silently.

Proposal

Add Lighthouse CI (treosh/lighthouse-ci-action or @lhci/cli) on PRs: build the site, serve public/, assert category budgets.

• Start with assertions as warnings, then ratchet to hard floors (e.g. Performance ≥ 0.90, Accessibility ≥ 0.95, SEO ≥ 0.95, Best-Practices ≥ 0.95) once the baseline is known.
• Covers OG/Twitter-card and meta validation for free via the SEO category.

Acceptance

• Lighthouse runs on PRs against the built site.
• lighthouserc.json with documented category thresholds.
• Baseline scores recorded; thresholds set just under baseline so regressions fail.