Refactor desktop UI to Buy/Sell XMR
Currently the desktop UI offers these options to buy/sell, where the asset being bought/sold depends on the context:

<img width="593" alt="image" src="https://github.com/user-attachments/assets/f68008fe-3e49-4a3b-b052-fae2f2bc780a">


This issue requests refactoring the desktop UI to be relative to always buying or selling XMR for other assets.

We need to decide exactly how the refactored UI should appear as part of this issue.