🤖 Add mdbook documentation with mermaid and CI/CD (#42)

## Overview

Sets up fast-building documentation using **mdbook** with mermaid
diagram support and automatic deployment to GitHub Pages.

## Features

- ✅ **mdbook** - Rust-based, blazingly fast builds
- ✅ **Mermaid diagrams** - Visual architecture documentation
- ✅ **Link checking** - Validates all links during build
- ✅ **GitHub Pages CI/CD** - Auto-deploys on push to main
- ✅ **Example pages** - Introduction, Getting Started, Architecture

## Commands Added

```bash
bun docs              # Serve with hot reload + open browser
bun docs:build        # Build static site
bun docs:watch        # Watch for changes
```

## CI/CD

- `.github/workflows/docs.yml` triggers on docs/ changes
- Deploys to https://ammarbandukwala.github.io/cmux
- Can be manually triggered

## Structure

```
docs/
├── book.toml           # Config (mermaid + linkcheck)
├── README.md           # Documentation for contributors
├── src/
│   ├── SUMMARY.md      # Table of contents
│   ├── intro.md
│   ├── getting-started.md
│   └── architecture.md # With mermaid diagrams
└── book/               # Build output (gitignored)
```

---
_Generated with `cmux`_

Author: ammario

.github/workflows/docs.yml

@@ -0,0 +1,59 @@
+name: Deploy Docs
+
+on:
+  push:
+    branches: ["main"]
+    paths:
+      - "docs/**"
+      - ".github/workflows/docs.yml"
+  workflow_dispatch: # Allow manual triggering
+
+# Sets permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Allow only one concurrent deployment
+concurrency:
+  group: "pages"
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup mdBook
+        uses: peaceiris/actions-mdbook@v2
+        with:
+          mdbook-version: "0.4.52"
+
+      - name: Install mdbook-mermaid
+        run: |
+          cargo install mdbook-mermaid --version 0.16.0
+          mdbook-mermaid install docs
+
+      - name: Install mdbook-linkcheck
+        run: cargo install mdbook-linkcheck --version 0.7.7
+
+      - name: Build docs
+        run: cd docs && mdbook build
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: ./docs/book
+
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4

.gitignore

@@ -62,6 +62,9 @@ release
 
 # Documentation
 docs/vercel/
+docs/book/
+docs/mermaid-init.js
+docs/mermaid.min.js
 
 # Secrets
 .env

AGENTS.md

@@ -1 +1 @@
-CLAUDE.md
+docs/src/AGENTS.md