feat(docs): wire AI-crawler baseline (preset 3.4.0 + validator + llms.txt)

[rubenvdlinde]

Summary

Wires the AI-crawler baseline that conduction-website shipped, so AI search bots (GPTBot, ClaudeBot, PerplexityBot, OAI-SearchBot, Claude-SearchBot, Google AI Overviews) can index this docs site to contract.

Changes

• docs/package.json: bump @conduction/docusaurus-preset to ^3.4.0; add postbuild + validate:ai-baseline scripts.
• docs/scripts/validate-ai-baseline.mjs: generic postbuild validator. Asserts robots.txt names an AI bot, llms.txt is shipped, sitemap exists, and per-page JSON-LD is present. Exits non-zero on failure so CI blocks regressions.
• docs/static/llms.txt: per-app intro paragraph plus the standard nav skeleton (Tutorials/Features/UseCases/Integrations/Technical/user-guide/api) and contact block.

References

• ci(documentation): run build/validate on PRs, deploy only on push .github#73 — preset-side rollout (ai-crawling plugin, llms.txt deliveries).
• feat(seo): AI-crawler baseline + content layer + validation gates conduction-website#55 — corporate-site reference implementation of the same gates.

Test plan

• CI green on this PR (postbuild validator runs during build).
• After merge + deploy, curl https://app-versions.conduction.nl/llms.txt returns the new file.
• curl https://app-versions.conduction.nl/robots.txt names at least one AI bot.