Adds a multi-step pipeline for generating per-extension documentation pages.
All scripts live in scripts/docs/ and are invoked via a single CLI entry point node scripts/docs/index.mjs <command>.

1. Deterministic extraction (pnpm docs:extract) — scans all extension directories, regex-parses TypeScript sources to collect nodes, marks, actions, keymaps, input rules, plugins, presets, options, and test examples into raw Markdown files + a JSON IR (docs-gen/raw/, docs-gen/extensions.json).
2. AI enrichment (three paths):
   • pnpm docs:enrich — calls OpenAI API directly (requires OPENAI_API_KEY)
   • scripts/docs/enrich-agent.md — a standalone instruction file you hand to a Cursor/Claude agent without any API key; the agent reads raw docs + source code and writes enriched files
   • pnpm docs:enrich:prompts + pnpm docs:enrich:apply — export prompts as JSON, process externally, apply responses
3. Assembly (pnpm docs:assemble) — merges enriched docs into docs-src/extensions/, patches toc.yaml and index.md.
4. Full build (pnpm docs:build) — runs generate → extract → assemble → Diplodoc in one command.
   ~70% of each page is filled deterministically from code; ~30% (description, syntax guide, serialization notes, use cases) is AI-generated.

New scripts