Update demo section in README to use video tag

Replaces the GIF demo with an embedded MP4 video using the HTML <video> tag for improved playback controls and quality.

Author: DongDuong2001

README.md

@@ -13,7 +13,7 @@
 
 ## Demo
 
-![Platform Demo](public/demo_video/Demo_Video.gif)
+<video src="public/demo_video/demo.mp4" controls width="100%"></video>
 
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