perf: responsive AVIF/WebP images; a11y contrast and link-text fixes

- scripts/optimize-images.mjs generates hashed AVIF/WebP variants at build time (sharp)
- Picture.astro + rehype plugin serve them via <picture> with srcset/sizes; hero gets fetchpriority=high
- footer CTA and active service-nav item meet WCAG AA contrast
- homepage Learn More link gets screen-reader-only context
- llms.txt: insights described as coming soon

docs/launch-checklist.md

@@ -140,7 +140,12 @@ not worth a force-push).
       sitemap but emits no `noindex` meta tag.
 - [ ] `article:published_time` / `article:modified_time` OG tags on insights posts.
 - [ ] `lastmod` in the sitemap from content dates.
-- [ ] Lighthouse ≥ 95 on SEO / Perf / Best-Practices / Accessibility.
+- [x] Lighthouse ≥ 95 (2026-10-23). Before, live mobile: Perf 82–86, A11y 95, SEO 92–100, LCP 4.3–4.9 s.
+      After (local build, mobile): Perf 96–99, A11y 100, SEO 100, LCP 1.8–2.4 s. Responsive AVIF/WebP via
+      `scripts/optimize-images.mjs` (runs in `npm run build`) + `components/Picture.astro` + a rehype plugin
+      for Markdown images; contrast fixes on the footer CTA and the active service-nav item; homepage
+      "Learn More" gets screen-reader context. New photos need no extra step: anything in
+      `public/assets/live-site/` gets variants; render it with `<Picture>` (or Markdown) to use them.
 - [ ] Umami/GA custom event for contact-form submits (today the `/thank-you/` pageview is the
       conversion signal).
 - [ ] Optional: move `bluecapstrategies.com` into Pangolin's `config.yml` `domains:` so it shows