Add generate_packs step before assets:precompile

The precompile check needs to run react_on_rails:generate_packs first
to generate the server-bundle-generated.js file that webpack imports.
This matches what other CI jobs do before running webpack builds.

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

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

Author: justin808

.github/workflows/precompile-check.yml

@@ -128,6 +128,8 @@ jobs:
           if ! bundle check --path=vendor/bundle; then
             bundle _2.5.9_ install --path=vendor/bundle --jobs=4 --retry=3
           fi
+      - name: Generate file system-based packs
+        run: cd react_on_rails/spec/dummy && RAILS_ENV=production bundle exec rake react_on_rails:generate_packs
       - name: Run assets:precompile and check output
         run: |
           cd react_on_rails/spec/dummy