fix: add React on Rails pack generation to CI workflow

- Add bundle exec rails react_on_rails:generate_packs step to JS CI
- Resolves missing server-bundle-generated.js error in CI builds
- Generated files are in .gitignore but needed for webpack builds

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ihabadham

.github/workflows/js_test.yml

@@ -44,5 +44,8 @@ jobs:
       - name: Build i18n libraries
         run: bundle exec rake react_on_rails:locale
 
+      - name: Generate React on Rails packs
+        run: bundle exec rails react_on_rails:generate_packs
+
       - name: Run js tests
         run: bundle exec rake ci:js