Unifiy Icon Button components

[josefinalliende]

Context

In PR #509 it was recommended to use CustomIconButton (lib/shared/custom_icon_button.dart) for buttons with just an icon. However, there is also a WnIconButton (lib/ui/core/ui/wn_icon_button.dart). Since we had already agreed in #382 to use the Wn prefix for shared UI components, having both creates confusion, makes it unclear which one should be used, and adds extra maintenance overhead.

Proposal

• Lets consolidate both into a single component named WnIconButton.
• Remove CustomIconButton and migrate all usages to WnIconButton