Add screenshot section to README

Added a placeholder for a screenshot in the README.

Author: tqviet1978

README.md

@@ -52,11 +52,9 @@ This makes it much easier to **prepare context for AI agents**.
 
 # Screenshot
 
-*(Add a screenshot here)*
-
-```
-docs/screenshot.png
-```
+<p align="center">
+  <img src="screenshot.png" width="900">
+</p>
 
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