Modernize GUI.sh interactive GUI menu system

[coelacant1]

Description

GUI.sh is a complex interactive GUI menu system (likely using whiptail or dialog) that has not been updated to the current framework standards. As a primary graphical entry point for users, it needs modernization to integrate properly with the shared utility framework.

Acceptance Criteria

• Script sources shared utilities consistently with other modernized scripts
• Menu navigation and script dispatch logic follows current conventions
• Compatible with remote execution workflows
• Existing menu structure and functionality preserved