Make formatting-only governance deterministic in CI

Change-source: pulse-maintainer

.github/workflows/canonical-governance.yml

@@ -86,6 +86,19 @@ jobs:
           cache: true
           cache-dependency-path: repos/pulse/go.sum
 
+      - name: Set up Node.js for frontend governance
+        uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
+        with:
+          node-version: '20'
+          cache: npm
+          cache-dependency-path: repos/pulse/frontend-modern/package-lock.json
+
+      - name: Install locked frontend governance dependencies
+        working-directory: repos/pulse/frontend-modern
+        env:
+          PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD: '1'
+        run: npm ci --ignore-scripts --no-audit --no-fund
+
       - name: Stub embedded frontend assets for Go tests
         run: bash scripts/ensure_test_assets.sh