🐛 `Button` has an unexpected border

When looking at the native counterparts of the `Button` widget, the fluent_ui implementation has a border that is not present in the Windows implementation.

This is what it currently looks lie:
<img width="150" height="54" alt="Image" src="https://github.com/user-attachments/assets/466f5415-e5e1-47b3-ae66-f1606bfd1066" />