make sure only admin users can use the preview mode

make sure only admin users can use the preview mode

compendium-frontend/src/helpers/usePreview.tsx

 import { useContext, useEffect } from "react";
 import { PreviewContext } from "./PreviewProvider";
 import { useSearchParams } from "react-router-dom";
+import { userContext } from "../shared/UserProvider";
 
 
 export function usePreview() {
     const { preview, setPreview } = useContext(PreviewContext);
+    const { user } = useContext(userContext);
     const [searchParams] = useSearchParams();
 
     const previewParameter = searchParams.get('preview');
 
     useEffect(() => {
-        if (previewParameter !== null) {
+        if (previewParameter !== null && user.permissions.admin) {
             setPreview(true);
         }
-    }, [previewParameter, setPreview]);
+    }, [previewParameter, setPreview, user]);
 
     return preview;
 }
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