ci(docs): auto-enable GitHub Pages on first run

The Docs workflow was failing on `actions/configure-pages@v5` with
"Get Pages site failed" because Pages isn't enabled on the repo
yet. Setting `enablement: true` lets the action auto-enable it so
the deploy can proceed without a manual Settings → Pages click.

.github/workflows/docs.yml

@@ -32,6 +32,10 @@ jobs:
           cd docs/book
           mdbook build
       - uses: actions/configure-pages@v5
+        with:
+          # Auto-enable Pages on the repo if not already configured.
+          # Without this, the action errors with "Get Pages site failed".
+          enablement: true
       - uses: actions/upload-pages-artifact@v3
         with:
           path: target/book