Add SEO content and structured metadata

[1337lean]

Summary

• add unique technical guides and FAQs for all 27 tool pages
• add search metadata, canonical URLs, JSON-LD, and generated Open Graph images
• make all tool pages statically generated while preserving target-prefill behavior
• stabilize sitemap dates, add canonical-host redirect handling, and prepare Cloudflare analytics
• document Search Console and deployment follow-up steps

Validation

• npm run lint
• npm run typecheck
• npm test (44 tests)
• npm run build (27/27 tool pages statically generated)