Upgrade React 17 to React 18

This workflow ensures you adopt React 18 safely, handling the new rendering semantics and strict mode quirks.

## Steps:

1. Update react and react-dom to version 18 in package.json.

2. Replace ReactDOM.render with createRoot in your entry file.

3. Audit StrictMode behavior and resolve double-render side effects.

4. Update Suspense boundaries and lazy-loaded components where needed.

5. Test hydration for server-rendered routes and fix mismatches.

6. Enable optional concurrent features on non-critical screens and measure impact.

7. Run visual regression tests to ensure no unexpected UI changes.