feat(seo): add broad entity and distribution layer

[Natsummerance]

Summary

• Enrich all 44 canonical pages with Organization, WebSite, WebPage, SoftwareApplication, Offer, screenshot, featureList, localized releaseNotes, license, publisher, language, and main-entity relationships.
• Add TechArticle entities to the four localized release-notes pages.
• Add a valid 44-entry full-site Atom feed linked from every page.
• Normalize Open Graph locale alternates and expand robots directives with snippet/video controls.
• Add security.txt, a noindex quality 404 recovery page, async image decoding, crawl-budget exclusions, and regenerated CSP JSON-LD hash.
• Turn these requirements into validator contracts and expand clean-network production checks to feed.xml, security.txt, and 404 behavior.

Approvals

Technical SEO / international distribution / trust quality: 9.89 / 9.86 / 9.82; final decision meeting 9.87 (broad_seo_approval.json).

Validation

• npm run verify:release: green across 44 canonical URLs and broad SEO contracts.
• Browser smoke: 44/44 routes passed, zero failures.
• Production workflow now validates Atom feed, security.txt, quality 404 behavior, all canonical routes, AI corpora, robots, sitemap, and PNG assets.