Add self-removal from WidgetManager in generated destructor

When app exits with a generated widget still in WidgetManager (e.g., user
closes window directly), LawnApp's destructor only cleans up known member
widgets (mGameSelector, mBoard, etc.). Unknown generated widgets remain
in WidgetManager's mWidgets list. When delete mWidgetManager runs,
~WidgetContainer() asserts mWidgets.empty().

Fix: add mWidgetManager->RemoveWidget(this) in generated destructor so
the widget removes itself from the manager before base destruction.
Combined with existing RemoveAllWidgets(false, false) and member
variable deletion, this ensures clean teardown in all paths.

Author: StackAndPointer

core/code_generator.py

@@ -285,6 +285,9 @@ def generate_cpp_for_interface(self, iface: Interface, project: Project) -> str:
         cpp += "}\n\n"
 
         cpp += f"{s.class_name}::~{s.class_name}()\n{{\n"
+        # If still attached to WidgetManager, remove self to prevent assertion in ~WidgetContainer()
+        cpp += "    if (mWidgetManager)\n"
+        cpp += "        mWidgetManager->RemoveWidget(this);\n"
         # Remove all child widgets from the container before deletion to satisfy WidgetContainer assertion
         cpp += "    RemoveAllWidgets(false, false);\n"
         for wid in iface.widgets.values():