docs: improve Pages SEO and product clarity

[paladini]

Summary

• rewrite the hero to explain exactly what team-ai-sync does before selling it
• add SEO metadata: canonical URL, robots meta, Twitter/Open Graph copy, SoftwareSourceCode JSON-LD, and FAQ JSON-LD
• add visible FAQ content for developer search intent
• add robots.txt and sitemap.xml for GitHub Pages

Validation

• npm run all
• git diff --check
• static SEO metadata check: title length, meta description length, canonical, robots, sitemap, and JSON-LD parsing
• desktop and mobile render checks via Edge headless