Update README with application description and image

Added an image and updated the description of the application.

Author: vuon9

README.md

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 A modern, all-in-one desktop application for developers featuring 45+ utilities for encoding, encryption, hashing, escaping, and data format conversions.
 
+<img width="1462" height="894" alt="image" src="https://github.com/user-attachments/assets/fd82c884-203d-44e0-a29d-a9f769eba33a" />
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 ## Features
 
 ### **Text Based Converter** (Unified Tool)