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.

docs/models/index.md

@@ -0,0 +1,25 @@
+# Choosing & Running Models
+
+RoboCo's agents are backend-agnostic. By default the whole workforce runs on **Anthropic Claude**, authenticated from the Claude Code session on your host — no API key to manage. You can route the company onto **xAI Grok** instead, or point individual agents and roles at **local / self-hosted** models, all from one page in the panel.
+
+<div class="grid cards" markdown>
+
+-   **[Provider routing](provider-routing.md)**
+
+    ---
+
+    The Settings → AI Providers page: the routing modes, agent-over-role-over-global precedence, saved keys, and the fail-soft fallback.
+
+-   **[Running on Grok](grok.md)**
+
+    ---
+
+    The whole workforce on xAI Grok via the official CLI and a SuperGrok subscription — no metered key.
+
+-   **[Resilience](resilience.md)**
+
+    ---
+
+    What keeps a run alive: crash auto-retry, and how rate limits and provider overloads park work instead of dropping it.
+
+</div>