s&box UI: Building HUD and menus with Razor PanelComponent — BuildHash, BindClass, StateHasChanged

In s&box, building HUD and menu UI requires Razor components (PanelComponent), not Unity-style OnGUI or uGUI. Developers don't know how to trigger re-renders, bind CSS classes dynamically, or structure the component lifecycle. BuildHash() is the key re-render trigger that many miss.