docs: add GitHub Pages documentation site

- 7-page docs site using just-the-docs Jekyll theme
- Covers spec format, CLI reference, config, GitHub Action, AI agents, architecture
- GitHub Actions workflow for auto-deploying on pushes to main
- Added docs site link in README header

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: corvid-agent

.github/workflows/docs.yml

@@ -0,0 +1,46 @@
+name: Deploy Docs
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'docs/**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Pages
+        uses: actions/configure-pages@v5
+
+      - name: Build with Jekyll
+        uses: actions/jekyll-build-pages@v1
+        with:
+          source: ./docs
+          destination: ./_site
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+
+  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