feat(docs): improve discoverability of API reference docs

[critesjosh]

Summary

• Sitemap augmentation: New augment_sitemap.js post-build script injects Aztec.nr API HTML URLs into sitemap.xml, making them visible to search engine crawlers (Docusaurus only indexes its managed routes)
• Typesense search config: Adds Aztec.nr API as a dedicated crawl target with custom selectors (api-nr) tuned for nargo doc HTML structure, enabling site search to surface API reference results
• LLM context files: Extends append_api_docs_to_llms.js to also include TypeScript API markdown docs in llms.txt / llms-full.txt, with format-aware processing (markdown passthrough vs HTML-to-text conversion)
• Governance parameter fixes: Corrects execution delay from 7 → 30 days, governance withdrawal delay from ~14.6 → ~38 days on mainnet, and adds clarification about GSE withdrawal delay during unstaking

Test plan

• yarn build completes successfully in docs/
• build/sitemap.xml contains aztec-nr-api/ URLs after build
• build/llms.txt contains both Aztec.nr and TypeScript API sections
• Typesense config validates (no JSON syntax errors)
• Governance parameters match on-chain values

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