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/fileEditor/AddFileCard.tsx

@@ -1,10 +1,10 @@
 import React, { useRef, useState } from "react";
-import { Button, Group, useMantineColorScheme } from "@mantine/core";
+import { Button, Group } from "@mantine/core";
 import { useTranslation } from "react-i18next";
 import AddIcon from "@mui/icons-material/Add";
 import { useFilesModalContext } from "@app/contexts/FilesModalContext";
 import LocalIcon from "@app/components/shared/LocalIcon";
-import { useLogoAssets } from "@app/hooks/useLogoAssets";
+import { Wordmark } from "@app/components/shared/Wordmark";
 import styles from "@app/components/fileEditor/FileEditor.module.css";
 import { useFileActionTerminology } from "@app/hooks/useFileActionTerminology";
 import { useFileActionIcons } from "@app/hooks/useFileActionIcons";
@@ -24,9 +24,7 @@ const AddFileCard = ({
   const { t } = useTranslation();
   const fileInputRef = useRef<HTMLInputElement>(null);
   const { openFilesModal } = useFilesModalContext();
-  const { colorScheme } = useMantineColorScheme();
   const [isUploadHover, setIsUploadHover] = useState(false);
-  const { wordmark } = useLogoAssets();
   const terminology = useFileActionTerminology();
   const icons = useFileActionIcons();
 
@@ -98,9 +96,9 @@ const AddFileCard = ({
         <div className={styles.addFileContent}>
           {/* Stirling PDF Branding */}
           <Group gap="xs" align="center">
-            <img
-              src={colorScheme === "dark" ? wordmark.white : wordmark.grey}
+            <Wordmark
               alt="Stirling PDF"
+              muted
               style={{ height: "2.2rem", width: "auto" }}
             />
           </Group>