add private functionality

frontend/app/(app)/code/[id]/page.tsx

@@ -82,6 +82,10 @@ export default async function CodePage({ params }: { params: { id: string } }) {
     return notFound()
   }
 
+  if (isSharedUser && sandboxData.visibility === "private") {
+    return notFound()
+  }
+
   return (
     <div className="overflow-hidden overscroll-none w-screen flex flex-col h-screen bg-background">
       <Room id={sandboxId}>