Fix Form Validation Bug in React + Node.js App

I have a small React + Node.js (Express) web app with a signup form that isn't working correctly. I need a developer to fix it quickly. The issue: The signup form on the frontend (React) allows submission even when the email field is empty or invalid. When the form is submitted, the Node.js/Express backend isn't returning proper error messages — it just sends a generic 500 error even for validation issues. I need proper validation added on both sides: frontend (show inline error messages) and backend (return clear 400 errors with a message for missing/invalid fields). Tech stack: Frontend: React (functional components, hooks) Backend: Node.js with Express Database: MongoDB (Mongoose) What I need done: Add frontend validation (required fields, valid email format) with error messages shown under each input. Add backend validation middleware (e.g., using express-validator or simple manual checks) that returns proper 400 status with clear error messages. Quick test to confirm both work together (bad input shows error, good input submits successfully).