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/how-to/01-the-company.md

@@ -4,7 +4,7 @@ What keeps twenty-two agents from dissolving into noise is that RoboCo is relent
 
 Work in RoboCo is always a **task**, and tasks nest into a tree that mirrors the org itself:
 
-```
+```text
 CEO (you, the human)
  ├── Intake (on-demand interviewer — drafts a task with you)
  ├── Secretary (your chief-of-staff — acts only on your command)

docs/how-to/05-the-business-workflow.md

@@ -52,4 +52,4 @@ The cleanest way to understand this layer is to walk it once, end to end:
 
 Previous: **[← The last call — and the loop](04-the-last-call-and-the-loop.md)** · Back to **[the index](README.md)**
 
-*RoboCo is early-stage, work-in-progress software (v0) — expect rough edges. The [README](../../README.md) covers setup, architecture, and the security model.*
+*RoboCo is early-stage, work-in-progress software (v0) — expect rough edges. The [Get Started guide](../get-started/index.md) covers setup, configuration, and the security model.*

docs/how-to/README.md

@@ -28,4 +28,4 @@ This guide follows one task — the Prompter's own build — from a rough idea t
 
 ---
 
-*RoboCo is early-stage, work-in-progress software (v0) — expect rough edges. The [README](../../README.md) covers setup, architecture, and the security model.*
+*RoboCo is early-stage, work-in-progress software (v0) — expect rough edges. The [Get Started guide](../get-started/index.md) covers setup, configuration, and the security model.*