Add SaaS frontend code (#5879)

# Description of Changes
Adds the code for the SaaS frontend as proprietary code to the OSS repo.
This version of the code is adapted from 22/1/2026, which was the last
SaaS version based on the 'V2' design. This will move us closer to being
able to have the OSS products understand whether the user has a SaaS
account, and provide the correct UI in those cases.

frontend/src/core/components/home/HomePageExtensions.tsx

@@ -0,0 +1,7 @@
+/**
+ * Core stub for HomePage extensions.
+ */
+
+export function HomePageExtensions() {
+  return null;
+}

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

@@ -28,6 +28,7 @@ import {
 } from '@app/components/shared/quickAccessBar/QuickAccessBar';
 import { Z_INDEX_OVER_FULLSCREEN_SURFACE } from '@app/styles/zIndex';
 import { QuickAccessBarFooterExtensions } from '@app/components/quickAccessBar/QuickAccessBarFooterExtensions';
+import { useConfigButtonIcon } from '@app/hooks/useConfigButtonIcon';
 
 const QuickAccessBar = forwardRef<HTMLDivElement>((_, ref) => {
   const { t } = useTranslation();
@@ -44,6 +45,8 @@ const QuickAccessBar = forwardRef<HTMLDivElement>((_, ref) => {
   const [configModalOpen, setConfigModalOpen] = useState(false);
   const [activeButton, setActiveButton] = useState<string>('tools');
   const scrollableRef = useRef<HTMLDivElement>(null);
+  const configButtonIcon = useConfigButtonIcon();
+
   const {
     tooltipOpen,
     manualCloseOnly,
@@ -202,7 +205,7 @@ const QuickAccessBar = forwardRef<HTMLDivElement>((_, ref) => {
     ...(shouldHideSettingsButton ? [] : [{
       id: 'config',
       name: t("quickAccess.settings", "Settings"),
-      icon: <LocalIcon icon="settings-rounded" width="1.25rem" height="1.25rem" />,
+      icon: configButtonIcon ?? <LocalIcon icon="settings-rounded" width="1.25rem" height="1.25rem" />,
       size: 'md' as const,
       type: 'modal' as const,
       onClick: () => {

frontend/src/core/components/shared/config/SettingsSearchBar.tsx

@@ -4,7 +4,7 @@ import { useTranslation } from 'react-i18next';
 import LocalIcon from '@app/components/shared/LocalIcon';
 import { NavKey, VALID_NAV_KEYS } from '@app/components/shared/config/types';
 import { Z_INDEX_OVER_CONFIG_MODAL } from '@app/styles/zIndex';
-import type { ConfigNavSection, ConfigNavItem } from '@core/components/shared/config/configNavSections';
+import type { ConfigNavSection, ConfigNavItem } from '@app/components/shared/config/configNavSections';
 
 interface SettingsSearchBarProps {
   configNavSections: ConfigNavSection[];

frontend/src/core/components/shared/config/configSections/GeneralSection.tsx

@@ -30,9 +30,11 @@ const BANNER_DISMISSED_KEY = "stirlingpdf_features_banner_dismissed";
 
 interface GeneralSectionProps {
   hideTitle?: boolean;
+  hideUpdateSection?: boolean;
+  hideAdminBanner?: boolean;
 }
 
-const GeneralSection: React.FC<GeneralSectionProps> = ({ hideTitle = false }) => {
+const GeneralSection: React.FC<GeneralSectionProps> = ({ hideTitle = false, hideUpdateSection = false, hideAdminBanner = false }) => {
   const { t } = useTranslation();
   const { preferences, updatePreference } = usePreferences();
   const { config } = useAppConfig();
@@ -156,7 +158,7 @@ const GeneralSection: React.FC<GeneralSectionProps> = ({ hideTitle = false }) =>
         </div>
       )}
 
-      {loginDisabled && !bannerDismissed && (
+      {!hideAdminBanner && loginDisabled && !bannerDismissed && (
         <Paper withBorder p="md" radius="md" style={{ background: "var(--mantine-color-blue-0)", position: "relative" }}>
           <ActionIcon
             variant="subtle"
@@ -215,7 +217,7 @@ const GeneralSection: React.FC<GeneralSectionProps> = ({ hideTitle = false }) =>
       )}
 
       {/* Update Check Section */}
-      {config?.appVersion && (
+      {!hideUpdateSection && config?.appVersion && (
         <Paper withBorder p="md" radius="md">
           <Stack gap="md">
             <div>