Enable QR Code Download

Description:
As a user, I want to download the QR code generated from the shortened URL so I can use it offline or share it easily.

Acceptance Criteria:

-    A "Download QR Code" button next to the generated QR code.
-    On click, the QR code should be downloaded as a high-quality image (e.g., PNG or JPG anything suitable format).
-   Proper file naming convention (e.g., shorturl-qr.png).