docs: publish llms.txt and llms-full.txt for agent-friendly ingestion

[teknium1]

Summary

Publish two agent-friendly entry points to the docs:

• /llms.txt — curated index, ~17 KB. Short description for each page, grouped by section mirroring the left sidebar. Safe to load directly into an LLM context window.
• /llms-full.txt — all 131 curated doc pages concatenated as markdown, ~1.8 MB. For one-shot ingestion by coding agents and RAG pipelines. Auto-generated skill pages are excluded (covered by the two catalog reference pages) to keep the file focused on the product.

Both files resolve at two URLs so either probing convention works:

• https://hermes-agent.nousresearch.com/llms.txt (classic root path)
• https://hermes-agent.nousresearch.com/docs/llms.txt (Docusaurus baseUrl)

What changed

• website/scripts/generate-llms-txt.py — new generator. ~80 curated pages organized into 10 sections (Getting Started, Using Hermes, Core Features, Automation, Media & Web, Messaging, Integrations, Guides, Developer Guide, Reference). Descriptions pulled from each page's frontmatter so the index stays current when docs are edited. All slugs validated against actual files on disk at generation time.
• website/scripts/prebuild.mjs — refactored into a small helper so skills.json and llms.txt generation share the python-spawn + graceful-fallback pattern. Non-fatal failure for llms.txt (site still builds).
• website/.gitignore — adds static/llms.txt and static/llms-full.txt (generated artifacts, same precedent as src/data/skills.json).
• .github/workflows/deploy-site.yml — Stage deployment step also copies both files to _site/ root so the classic /llms.txt URL works, not just /docs/llms.txt.
• website/docs/index.md — adds a "For LLMs and coding agents" section linking to both files.

Motivation

Matt Palmer flagged the docs as "agent unfriendly — no llms.txt / llms-full.txt." Fair critique. Conforms to the emerging llmstxt.org spec.

Validation

cd website && npm run build

Wrote website/static/llms.txt (17,092 bytes)
Wrote website/static/llms-full.txt (1,874,374 bytes)
[SUCCESS] Generated static files in "build".

Only warning is the pre-existing broken anchor in adding-platform-adapters (unrelated, same as every recent docs PR).

Maintenance

To add a new section or page to the curated index, edit the SECTIONS list in generate-llms-txt.py. Missing slugs will fail the prebuild loudly.