Global function (BackgroundBlurCornerRadiusByScreenSize) that dynamically adjusts the corner radius of all background blur elements based on the current viewport dimensions. The function calculates a scaling factor using a reference resolution (e.g., 1920×1080) and applies it to a base corner radius value to ensure consistent visual appearance across different screen sizes. This function is called from the Game Instance (OnWindowSizeChanged) and broadcasts to all relevant widgets via Blueprint Interface
