MonoGame UI XAML-style Grid layout — row and column definitions with pixel (fixed), auto (content-sized), and star (*) proportional sizing. Children are placed at specific Grid.Row / Grid.Column coordinates with optional span. Use this skill whenever the user asks about a grid layout, table layout, XAML Grid, rows and columns in UI, grid with star sizing, proportional columns, "how do I arrange UI elements in a table", or any 2D grid layout in MonoGame UI.
