Remove generated .res.js files from git and add to .gitignore

Generated ReScript files (.res.js, .res.mjs) are build artifacts that
should not be committed to version control. They are automatically
generated from .res source files during the build process.

Changes:
- Removed all .res.js files from git tracking
- Added **/*.res.js and **/*.res.mjs to .gitignore
- These files will be generated during yarn res:build

Similar to how we ignore other build artifacts like:
- **/generated/** (React on Rails generated packs)
- /ssr-generated/ (SSR bundles)
- /public/packs (Webpack/Rspack output)

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

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

Author: justin808

.gitignore

@@ -60,4 +60,8 @@ client/app/bundles/comments/rescript/**/*.bs.js
 # Generated React on Rails packs
 **/generated/**
 
+# Generated ReScript files (compiled from .res source files)
+**/*.res.js
+**/*.res.mjs
+
 .claude/