Add JSON-LD structured data to docs pages

[AvdLee]

Summary

• Adds TechArticle JSON-LD schema to all documentation pages for better search engine understanding
• Adds BreadcrumbList JSON-LD schema derived from the URL path hierarchy
• Adds FAQPage JSON-LD schema on the FAQ page to enable rich results in Google Search

Changes

• Modified docs/src/components/starlight/Head.astro to generate and inject structured data

Test plan

• Verify npm run build passes
• Check a docs page source for TechArticle + BreadcrumbList JSON-LD
• Check the FAQ page source for FAQPage JSON-LD
• Validate schemas at https://search.google.com/test/rich-results