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/desktop/components/shared/config/configNavSections.tsx

@@ -8,6 +8,8 @@ import { SaaSTeamsSection } from '@app/components/shared/config/configSections/S
 import { connectionModeService } from '@app/services/connectionModeService';
 import { authService } from '@app/services/authService';
 
+export type { ConfigNavSection, ConfigNavItem } from '@core/components/shared/config/configNavSections';
+
 /**
  * Hook version of desktop config nav sections with proper i18n support
  */