fix(frontend): use useSupabase() hook instead of raw store

The useSupabaseStore requires initialization via useSupabase() hook
which sets up the API client, router, and fetches the user. Using
the raw store directly meant user was always null on the link page.

Also wait for isUserLoading before deciding auth state to avoid
flashing the not-authenticated view.

autogpt_platform/frontend/src/app/(no-navbar)/link/[token]/page.tsx

@@ -3,7 +3,7 @@
 import { Button } from "@/components/atoms/Button/Button";
 import { AuthCard } from "@/components/auth/AuthCard";
 import { Text } from "@/components/atoms/Text/Text";
-import { useSupabaseStore } from "@/lib/supabase/hooks/useSupabaseStore";
+import { useSupabase } from "@/lib/supabase/hooks/useSupabase";
 import { CheckCircle, LinkBreak, Spinner } from "@phosphor-icons/react";
 import { useParams } from "next/navigation";
 import { useEffect, useState } from "react";
@@ -30,7 +30,7 @@ type LinkState =
 export default function PlatformLinkPage() {
   const params = useParams();
   const token = params.token as string;
-  const { user, supabase } = useSupabaseStore();
+  const { user, supabase, isUserLoading } = useSupabase();
 
   const [state, setState] = useState<LinkState>({ status: "loading" });
 
@@ -39,13 +39,15 @@ export default function PlatformLinkPage() {
   // separate status call (which requires bot API key anyway).
   useEffect(() => {
     if (!token) return;
+    // Wait for Supabase to finish loading before deciding auth state
+    if (isUserLoading) return;
 
     if (!user) {
       setState({ status: "not-authenticated" });
     } else {
       setState({ status: "ready" });
     }
-  }, [token, user]);
+  }, [token, user, isUserLoading]);
 
   async function handleLink() {
     if (!supabase) return;