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/proprietary/routes/login/LoggedInState.tsx

@@ -2,13 +2,12 @@ import { useEffect } from "react";
 import { useNavigate } from "react-router-dom";
 import { useAuth } from "@app/auth/UseSession";
 import { useTranslation } from "react-i18next";
-import { useLogoPath } from "@app/hooks/useLogoPath";
+import { LogoIcon } from "@app/components/shared/LogoIcon";
 
 export default function LoggedInState() {
   const navigate = useNavigate();
   const { user } = useAuth();
   const { t } = useTranslation();
-  const logoPath = useLogoPath();
 
   useEffect(() => {
     const timer = setTimeout(() => {
@@ -47,8 +46,7 @@ export default function LoggedInState() {
               justifyContent: "center",
             }}
           >
-            <img
-              src={logoPath}
+            <LogoIcon
               alt="Stirling PDF Logo"
               style={{ width: "64px", height: "64px", objectFit: "contain" }}
             />

frontend/src/proprietary/routes/login/LoginHeader.tsx

@@ -1,4 +1,4 @@
-import { useLogoAssets } from "@app/hooks/useLogoAssets";
+import { Wordmark } from "@app/components/shared/Wordmark";
 
 interface LoginHeaderProps {
   title: string;
@@ -11,18 +11,12 @@ export default function LoginHeader({
   subtitle,
   centerOnly = false,
 }: LoginHeaderProps) {
-  const { wordmark } = useLogoAssets();
-
   return (
     <div
       className={`login-header${centerOnly ? " login-header-centered" : ""}`}
     >
       <div className="login-header-logos">
-        <img
-          src={wordmark.black}
-          alt="Stirling PDF"
-          className="login-logo-text"
-        />
+        <Wordmark alt="Stirling PDF" className="login-logo-text" />
       </div>
       {title && <h1 className="login-title">{title}</h1>}
       {subtitle && <p className="login-subtitle">{subtitle}</p>}