feat(seo): expand structured data with shared jsonld helpers (#126)

[Escelit]

Summary

Generalizes the ad-hoc Article JSON-LD in CaseStudies.tsx into a typed src/utils/jsonld.ts helper module and closes the structured-data coverage gaps across the site.

Changes

• New src/utils/jsonld.ts: typed helpers organization(), article(), faqPage(), howTo(), breadcrumbList() (plus exported SITE_URL).
• CaseStudies.tsx: refactored to consume article() + now emits a BreadcrumbList on /case-studies/:slug.
• Blog.tsx: emits an Article per blog post (from MDX frontmatter) + BreadcrumbList on both the list and /blog/:slug.
• Faq.tsx: emits a FAQPage built from src/data/faq.json.
• Grants.tsx: emits a HowTo for the grant application steps derived from wave.
• New BlogAuthor.tsx + /blog/author/:id route: emits a BreadcrumbList (closes the third nested-route gap).
• scripts/validate-jsonld.mjs: rebuilds every emitted blob from real data and validates it against a local schema.org structural validator. Wired into CI via pnpm validate:jsonld.

Acceptance

• Every blog post emits a valid Article block
• /faq emits a valid FAQPage block with every Q&A
• Nested routes emit BreadcrumbList (/case-studies/:slug, /blog/:slug, /blog/author/:id)
• Validator script exits 0 in CI
• Build passes (tsc + vite build green)
• Lighthouse SEO unchanged (adds structured data only)

Test plan

• pnpm validate:jsonld → all 8 blobs valid, exits 0
• pnpm build → green
• pnpm format:check → clean

Closes #126

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[truthixify]

Thanks @Escelit. Conflicts on src/pages/Blog.tsx against #136.

This is the last of the three in the order I suggested on #138, since the BreadcrumbList here covers the /blog/author/:id route that #138 adds. Worth rebasing after those two land so you only do it once.