Replace placeholder image with actual screenshot

Updated the image in the README to a new screenshot.

Author: SyntaxSidekick

README.md

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 A modern, interactive web application for practicing JavaScript concepts through randomized coding challenges. Perfect for developers looking to improve their JavaScript knowledge with hands-on practice.
 
-![JS Challenge Lab Screenshot](https://via.placeholder.com/800x400/3b82f6/ffffff?text=JS+Challenge+Lab)
+<img width="1917" height="915" alt="js-learning-lab" src="https://github.com/user-attachments/assets/0dfe90e9-fc87-449e-9240-06529831889b" />
 
 ## ✨ Features