Recover the public Knowledgebase landing

[sarthakagrawal927]

Closes #28

What changed

• restores an independently buildable static public landing under landing-astro/
• keeps the Access-protected dashboard and RAG Worker outside the public package
• derives the HTML route, substantive Markdown, /api/ai, llms.txt, robots, and HTML-only sitemap from one typed route registry
• adds deterministic public-boundary and catalog coverage checks
• upgrades the new package to Astro 7.1.6 and pins patched Sharp 0.35.0; dependency audit reports zero known vulnerabilities
• archives the completed OpenSpec and records the source-ready status without claiming deployment

Validation

• cd landing-astro && pnpm run check
• cd landing-astro && pnpm audit --audit-level high
• Fleet agent audit against a canonical-host local build: S-tier, 10/10 checks, 100% route Markdown coverage, 100% catalog integrity
• openspec validate --all --strict
• design workflow: preserve lane, critique 36/40, audit 19/20, zero unresolved P0/P1
• git diff --check

No Pages configuration, production deployment, Worker route, credential, or private corpus data was changed.

[cloudflare-workers-and-pages]

Deploying knowledgebase-landing with    Cloudflare Pages

Latest commit:	6b9ce98
Status:	✅  Deploy successful!
Preview URL:	https://7b6fd968.knowledgebase-landing.pages.dev
Branch Preview URL:	https://agent-recover-public-landing.knowledgebase-landing.pages.dev

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