Build CSS in CI instead of checking it is up-to-date

Since compiled.css is no longer tracked in the repository, the CI
needs to build it before running tests. Move the Node.js setup and
CSS build steps before the test step.

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

Author: hsbt

.github/workflows/ci.yml

@@ -24,22 +24,20 @@ jobs:
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           fetch-depth: 1
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@3ff19f5e2baf30647122352b96108b1fbe250c64 # v1.299.0
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
           node-version: '20'
           cache: 'npm'
       - name: Install npm dependencies
         run: npm ci
-      - name: Check CSS is up-to-date
-        run: |
-          npm run build-css
-          git diff --exit-code stylesheets/compiled.css || (echo "Error: compiled.css is out of date. Run 'npm run build-css' and commit the changes." && exit 1)
-      - name: Setup Ruby
-        uses: ruby/setup-ruby@3ff19f5e2baf30647122352b96108b1fbe250c64 # v1.299.0
-        with:
-          ruby-version: ${{ matrix.ruby }}
-          bundler-cache: true
+      - name: Build CSS
+        run: npm run build-css
       - name: Dump Ruby version
         run: ruby -v
       - name: Run tests