Fix GitHub Actions formatting error by excluding pro directory

Add react_on_rails_pro/ to .prettierignore to prevent prettier from checking
pro package files during core package linting in GitHub Actions.

Fixes: https://github.com/shakacode/react_on_rails/actions/runs/18015295891/job/51258566516

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

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

Author: AbanoubGhadban

.prettierignore

@@ -1,5 +1,7 @@
 node_modules/
 package.json
+# Exclude pro package (has its own formatting)
+react_on_rails_pro/
 tmp/
 coverage/
 **/app/assets/webpack/