Fix TeamSnap callback stalls

frontend/src/pages/SignInPage.tsx

@@ -1,12 +1,14 @@
 import { useState } from "react";
-import { useLocation, useNavigate } from "react-router-dom";
+import { useLocation, useNavigate, useSearchParams } from "react-router-dom";
 
 import { api } from "../api/client";
 
 export function SignInPage() {
   const navigate = useNavigate();
   const location = useLocation();
+  const [searchParams] = useSearchParams();
   const [error, setError] = useState<string | null>(null);
+  const callbackError = searchParams.get("error");
 
   async function handleTeamSnapStart() {
     try {
@@ -46,10 +48,10 @@ export function SignInPage() {
             </div>
           </div>
         </div>
-        {error ? (
+        {error || callbackError ? (
           <div className="col-12 col-md-8 col-lg-5 col-xl-4">
             <div className="alert alert-danger mb-0" role="alert">
-              {error}
+              {error ?? callbackError}
             </div>
           </div>
         ) : null}