fix(icons): rebuild dist/index.js in ESM format and allow in git

- Rebuilt dist/index.js as ESM (not CJS) for Vite/Rollup compatibility
- Added exception to .gitignore to track icons dist folder
- Fixes 'Icon is not exported' build error on Railway

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

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: jog1t

.gitignore

@@ -26,6 +26,7 @@ pnpm-debug.log*
 # TypeScript
 *.tsbuildinfo
 dist/
+!frontend/packages/icons/dist/
 
 # IDE
 .vscode/