Fix general settings route and req.user references

- Update frontend settings service to use correct /api/admin/settings/general route
- Fix all req.user to req.admin references in adminSettings.js
- Ensures settings can be saved without authentication errors

frontend/src/components/admin/AdminAuthWrapper.tsx

@@ -0,0 +1,13 @@
+import React from 'react';
+import { Outlet } from 'react-router-dom';
+import { AdminAuthProvider } from '../../contexts';
+
+export const AdminAuthWrapper: React.FC = () => {
+  return (
+    <AdminAuthProvider>
+      <Outlet />
+    </AdminAuthProvider>
+  );
+};
+
+AdminAuthWrapper.displayName = 'AdminAuthWrapper';