Widget::get_parent() dereferences nullptr for the root Screen #24

Where: Source/Widgets/ctui_widget.cpp:17-20, Source/Widgets/ctui_widget.h:24,32-36

const Widget& Widget::get_parent() const { return *_parent; }

_parent is set to nullptr in the Widget() constructor and never overwritten for the Screen singleton (it's the root, has no parent). Calling get_parent() on screen (or any orphaned widget) dereferences a null pointer through a reference — UB.

Suggested fix: either guard/assert for the root case, or change the return type to something that can represent "no parent" (Widget*/std::optional<std::reference_wrapper<Widget>>).

Suggested branch: fix/widget-get-parent-root
Suggested PR title: fix(widget): guard get_parent() against null root parent