Add ReScript build step before assets:precompile

The dummy app uses ReScript components that need to be compiled before
webpack can bundle them. This adds `pnpm run build:rescript` to compile
HelloWorldReScript.res.js and other ReScript files.

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

Co-Authored-By: Claude <[email protected]>

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: Build ReScript files
+        run: cd react_on_rails/spec/dummy && pnpm run build:rescript
       - 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