Update image source for digital data icon

Modified the `src` attribute of an `<img>` element in `app.tsx` to replace the previous image with a new icon located at "/assets/images/dd-button-icon.webp". This change enhances the visual representation of the application by using a more relevant image.

src/client/dd-hub-react/src/app.tsx

@@ -37,7 +37,7 @@ export default function App({ children }: AppProps) {
       }}
     >
       <img
-        src="/assets/images/product/product-default.webp"
+        src="/assets/images/dd-button-icon.webp"
         alt="Digital Data"
       />
     </Fab>