🔧 Beyond localhost:3000: How to Finally Connect Your Frontend and Backend

If you're learning full-stack development, you've probably been here before:

You've built a beautiful React frontend. You've created a powerful Express.js backend. You start both servers - frontend on localhost:3000, backend on localhost:5000 - and then... CORS error.

That dreaded red message in the console:

text
Access to fetch at...