To rotate the gradient you can e.g use the ‘gradientTransform’ attribute, like this:
<?xml version="1.0" ?>
<svg xmlns="http://www.w3.org/2000/svg" width="100%" height="100%"
viewBox="0 0 1 1" preserveAspectRatio="none">
<linearGradient id="grad-ucgg-generated" gradientUnits="userSpaceOnUse"
x1="0%" y1="0%" x2="100%" y2="0%" gradientTransform="rotate(65)">
<stop offset="0%" stop-color="#ffffff" stop-opacity="0"/>
<stop offset="100%" stop-color="#ff0000" stop-opacity="1"/>
</linearGradient>
<rect x="0" y="0" width="1" height="1" fill="url(#grad-ucgg-generated)" />
</svg>