chore(website): retire stale whitepaper downloads

[blove]

Summary

• Retire stale generated whitepaper PDFs/previews and remove the obsolete LLM-based whitepaper generator script.
• Replace public PDF download CTAs/emails with refreshed-guide signup copy and current docs links.
• Add website e2e coverage to prevent marketing pages from linking retired PDF assets.

Validation

• rg -n "whitepapers/(angular|chat|render)\\.pdf|whitepaper\\.pdf|whitepaper-preview|generate-whitepaper|Download the Guide|Download PDF|download directly|AgentRef|createMockAgentRef|injectAgentRef|MockStreamTransport|streamResource\\(|provideStreamResource|@cacheplane/angular|@cacheplane/chat|@cacheplane/render" apps/website/src apps/website/emails apps/website/public apps/website/scripts package.json --glob '!**/api-docs.json' --glob '!**/tsconfig.tsbuildinfo' (no matches)
• npx nx lint website --skip-nx-cache (passes; existing instrumentation-client non-null warning remains)
• npx vitest run apps/website/src/lib/docs.spec.ts
• npx nx e2e website --skip-nx-cache
• npx nx build website --skip-nx-cache
• git diff --check

[vercel]

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Project	Deployment	Actions	Updated (UTC)
cacheplane	Ready	Preview, Comment	May 7, 2026 5:47pm