Improve user session handling in middleware

The changes add user session handling directly in the middleware. This ensures the user data is fetched at the start of a request and then passed on to route handlers, reducing repeated data fetching. Also, these improvements include adjustments for how sign-out and auth-change events are managed, particularly when the user session state changes. Additionally, it corrects the error response from useUser hook to return `undefined` instead of `null`.

packages/supabase/src/hooks/use-sign-out.ts

@@ -1,15 +1,13 @@
-import { useMutation, useQueryClient } from '@tanstack/react-query';
+import { useMutation } from '@tanstack/react-query';
 
 import { useSupabase } from './use-supabase';
 
 export function useSignOut() {
   const client = useSupabase();
-  const queryClient = useQueryClient();
 
   return useMutation({
     mutationFn: async () => {
       await client.auth.signOut();
-      await queryClient.invalidateQueries();
     },
   });
 }