Add redirect logic to login and signup pages for logged-in users

Co-authored-by: vincanger <70215737+vincanger@users.noreply.github.com>

template/app/src/auth/LoginPage.tsx

@@ -1,8 +1,19 @@
-import { LoginForm } from "wasp/client/auth";
+import { useEffect } from "react";
+import { useNavigate } from "react-router-dom";
+import { LoginForm, useAuth } from "wasp/client/auth";
 import { Link as WaspRouterLink, routes } from "wasp/client/router";
 import { AuthPageLayout } from "./AuthPageLayout";
 
 export default function Login() {
+  const { data: user } = useAuth();
+  const navigate = useNavigate();
+
+  useEffect(() => {
+    if (user) {
+      navigate("/demo-app");
+    }
+  }, [user, navigate]);
+
   return (
     <AuthPageLayout>
       <LoginForm />

template/app/src/auth/SignupPage.tsx

@@ -1,8 +1,19 @@
-import { SignupForm } from "wasp/client/auth";
+import { useEffect } from "react";
+import { useNavigate } from "react-router-dom";
+import { SignupForm, useAuth } from "wasp/client/auth";
 import { Link as WaspRouterLink, routes } from "wasp/client/router";
 import { AuthPageLayout } from "./AuthPageLayout";
 
 export function Signup() {
+  const { data: user } = useAuth();
+  const navigate = useNavigate();
+
+  useEffect(() => {
+    if (user) {
+      navigate("/demo-app");
+    }
+  }, [user, navigate]);
+
   return (
     <AuthPageLayout>
       <SignupForm />