ci: Add GitHub Actions workflow for docs deployment

Builds Verso documentation and deploys to GitHub Pages on push to main.

After pushing, enable GitHub Pages in repo settings:
Settings > Pages > Source: GitHub Actions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: alok

.github/workflows/docs.yml

@@ -0,0 +1,63 @@
+name: Build and Deploy Docs
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: "pages"
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install elan
+        run: |
+          curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh -s -- -y --default-toolchain none
+          echo "$HOME/.elan/bin" >> $GITHUB_PATH
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Get Mathlib cache
+        run: lake exe cache get || true
+
+      - name: Build LeanPlot
+        run: lake build
+
+      - name: Build documentation
+        run: lake build leanplot-docs
+
+      - name: Generate documentation
+        run: .lake/build/bin/leanplot-docs
+
+      - name: Setup Pages
+        uses: actions/configure-pages@v4
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: '_out/docs/html-multi'
+
+  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