🐛 `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:

Start by locating the Flutter Button widget and compare its rendered border with the Windows native counterpart shown in the issue. The work is done when the fluent_ui Button no longer displays the unexpected border and visually matches the Windows implementation.

Written by the indexing model from the issue text.