fix(web): finish launch readiness pass

[EmersonBraun]

Summary

• finish the AgentsKit and Registry launch-readiness polish
• normalize semantic landmarks, touch targets, focus states, metadata, and responsive behavior
• refresh the deterministic knowledge artifact after the landing updates

Validation

• complete quality gates and monorepo build pass
• docs and registry focused tests/builds pass
• Vercel previews remain disabled for this branch

[github-actions]

Lighthouse

URL	Performance	Accessibility	Best practices	SEO
http://127.0.0.1:3000/	54	92	96	100
http://127.0.0.1:3000/docs	66	100	96	100
http://127.0.0.1:3000/docs/get-started/getting-started/quickstart	66	96	96	100
http://127.0.0.1:3000/stack	92	100	96	100
http://127.0.0.1:3000/showcase	92	100	96	100

Run by .github/workflows/lighthouse.yml.