docs: add the user-facing MkDocs documentation site

Build a complete user-facing documentation site (MkDocs Material) under docs/, served at roboco.dev/docs via a new gh-pages deploy workflow.

- Sections: Get Started, The Company, the Tour, Operating the Panel, Choosing & Running Models, Cost & Observability, Optional Subsystems, Configure & Deploy, API Reference, Troubleshooting & Security (55 pages).
- mkdocs.yml (Material theme; excludes the agent-facing rag/ corpus, internal scratch, and orphaned stub trees) and .github/workflows/docs.yml (mkdocs gh-deploy to gh-pages).
- Retire the stale root usage.md and deployment.md to redirect stubs into the site.
- Fix the docs tooling: add the pymarkdownlnt dependency + .pymarkdown.json, run serve-docs/lint-docs/fix-docs under the docs extra, add a build-docs strict gate.
- Fix the roboco console-script entry point (cli, not the un-awaited async main).
- README: correct the project-structure tree (optimal.py, alembic) and link the docs site.

CLAUDE.md

@@ -536,4 +536,4 @@ ROBOCO_OLLAMA_BASE_URL=http://roboco-ollama:11434          # Native API
 
 ## Blueprint Reference
 
-The organizational structure, communication matrix, role descriptions, and access-control model are documented inline above and in the published `docs/` tree (per-area `README.md` files, `usage.md`, `deployment.md`).
+The organizational structure, communication matrix, role descriptions, and access-control model are documented inline above and in the user-facing documentation site (MkDocs Material; source under `docs/`, built by `mkdocs.yml`, published to `gh-pages` via `.github/workflows/docs.yml` and served at roboco.dev/docs). `docs/rag/` remains the agent-facing RAG corpus (excluded from the published site); the old root `usage.md` / `deployment.md` are now redirect stubs into the site.