fix: remove nested html/ from mdBook output before deploy

The mdBook [output.html] config creates a book/html/ subdirectory
that was being deployed alongside the site, causing gh-pages:docs/
to contain html/ instead of the site files directly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jeffabailey

.github/workflows/mdbook.yml

@@ -74,6 +74,9 @@ jobs:
       - name: Build with mdBook
         run: ${{ env.CARGO_HOME }}/bin/mdbook build
 
+      - name: Remove nested html output
+        run: rm -rf ./book/html
+
       - name: Deploy to GitHub Pages
         uses: JamesIves/github-pages-deploy-action@v4
         with:
@@ -148,6 +151,10 @@ jobs:
         if: github.event.action != 'closed'
         run: ${{ env.CARGO_HOME }}/bin/mdbook build
 
+      - name: Remove nested html output
+        if: github.event.action != 'closed'
+        run: rm -rf ./book/html
+
       - name: Deploy PR preview
         uses: rossjrw/pr-preview-action@v1
         with: