greyBox method
Wraps the widget in a ColoredBox with system grey color.
Uses CupertinoColors.systemGrey which adapts to light/dark mode. This is the standard grey color used throughout iOS interfaces, commonly used for secondary text, disabled states, or neutral elements.
Returns a ColoredBox containing the current widget with grey background.
Example:
Text('Disabled').greyBox()
Implementation
ColoredBox greyBox() => coloredBox(CupertinoColors.systemGrey);