fix(auth): useAuth() hook in AppShell/StartLayout + is_system_admin in login response

frontend/src/components/layout/AppShell.tsx

@@ -15,9 +15,11 @@ import { WelcomeDialog } from '@/components/onboarding/WelcomeDialog';
 import { OnboardingTour } from '@/components/onboarding/OnboardingTour';
 import { CommandPalette } from '@/components/search/CommandPalette';
 import { useOnboardingStore } from '@/store/onboardingStore';
+import { useAuth } from '@/hooks/useAuth';
 
 export function AppShell() {
   const location = useLocation();
+  useAuth();
 
   // Track context for AI Proactive suggestions
   useAIContext();

frontend/src/components/layout/StartLayout.tsx

@@ -10,8 +10,10 @@ import { PluginRegistry } from '@/components/plugins/PluginRegistry';
 import { ErrorBoundary } from '@/components/common/ErrorBoundary';
 import { Outlet } from 'react-router-dom';
 import { CommandPalette } from '@/components/search/CommandPalette';
+import { useAuth } from '@/hooks/useAuth';
 
 export function StartLayout() {
+  useAuth();
   return (
     <div className="flex h-screen overflow-hidden bg-secondary-50" data-testid="start-layout">
       <PluginRegistry />