fix(ci): restore Dart Sass install step (#170)

Docsy v0.17.0 requires Dart Sass, which Hugo invokes as the `sass`
executable on PATH. The GitHub runner does not pick up the
sass-embedded npm binary from node_modules the way local builds do, so
the theme's SCSS fails to transpile. Reinstate the snap install; the
sass-embedded devDependency stays for zero-setup local development.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: Arthurvdv

.github/workflows/hugo.yaml

@@ -37,6 +37,8 @@ jobs:
         run: |
           wget -O ${{ runner.temp }}/hugo.deb https://github.com/gohugoio/hugo/releases/download/v${HUGO_VERSION}/hugo_extended_${HUGO_VERSION}_linux-amd64.deb \
           && sudo dpkg -i ${{ runner.temp }}/hugo.deb
+      - name: Install Dart Sass
+        run: sudo snap install dart-sass
       - name: Checkout
         uses: actions/checkout@v7
         with: