Chore/remove usage of mantine color scheme (#6108)

Remove instances of `colorScheme === "dark" ?` in the app and rely on
the theme.css' light and dark variables instead.

frontend/src/core/components/shared/LogoIcon.tsx

@@ -0,0 +1,14 @@
+import React from "react";
+import { useMantineColorScheme } from "@mantine/core";
+import { useLogoPath } from "@app/hooks/useLogoPath";
+
+interface LogoIconProps extends React.ImgHTMLAttributes<HTMLImageElement> {
+  alt?: string;
+}
+
+export function LogoIcon({ alt = "", ...props }: LogoIconProps) {
+  const { colorScheme } = useMantineColorScheme();
+  const logoPaths = useLogoPath();
+  const src = colorScheme === "dark" ? logoPaths.dark : logoPaths.light;
+  return <img src={src} alt={alt} {...props} />;
+}