Remove non-existent AdminSystemDashboard import and route

The AdminSystemDashboard file doesn't exist in the codebase and was causing
a 500 error. Removed the lazy import and route that referenced it.

This aligns with the recent removal of the aws-admin pattern from the backend.

frontend/src/App.tsx

@@ -69,9 +69,6 @@ const AccountSettingsPage = lazy(() => import("./pages/account/AccountSettingsPa
 const TeamManagementPage = lazy(() => import("./pages/account/TeamManagementPage"));
 const UsageAnalyticsPage = lazy(() => import("./pages/account/UsageAnalyticsPage"));
 
-// Admin Module - Only dashboard for aws-admin users
-const AdminSystemDashboard = lazy(() => import("./pages/admin/AdminSystemDashboard"));
-
 // Reference Data - Lazy loaded
 const SeedKeywords = lazy(() => import("./pages/Reference/SeedKeywords"));
 const ReferenceIndustries = lazy(() => import("./pages/Reference/Industries"));
@@ -277,13 +274,6 @@ export default function App() {
             <Route path="/account/team" element={<TeamManagementPage />} />
             <Route path="/account/usage" element={<UsageAnalyticsPage />} />
             
-            {/* Admin Routes - Only Dashboard for aws-admin users */}
-            <Route path="/admin/dashboard" element={
-              <AwsAdminGuard>
-                <AdminSystemDashboard />
-              </AwsAdminGuard>
-            } />
-            
             {/* Reference Data */}
             <Route path="/reference/seed-keywords" element={<SeedKeywords />} />
             <Route path="/planner/keyword-opportunities" element={<KeywordOpportunities />} />