Fix: AddAccount layout scrolling issue

[gioisco]

Summary: Refactored the AddAccount screen layout to resolve scrolling issues.

Changes:

• Replaced Stack with Column to streamline vertical arrangement.
• Wrapped the SingleChildScrollView component with Expanded.
• Ensured the confirmation button remains visible and does not overlap with scrollable content.
• Enhanced user experience by making sure the input fields and options are fully accessible without obstruction.

Screenshots:

After attempt to scroll.

• Before:

• After: