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 />

template/app/src/payment/stripe/webhook.ts

@@ -141,7 +141,7 @@ async function handleInvoicePaid(
 
 function getInvoicePriceId(invoice: Stripe.Invoice): Stripe.Price["id"] {
   const invoiceLineItems = invoice.lines.data;
-  // We only expect one line item. 
+  // We only expect one line item.
   // If your workflow expects more, you should change this function to handle them.
   if (invoiceLineItems.length !== 1) {
     throw new Error("There should be exactly one line item in Stripe invoice");
@@ -204,7 +204,7 @@ function getSubscriptionPriceId(
   subscription: Stripe.Subscription,
 ): Stripe.Price["id"] {
   const subscriptionItems = subscription.items.data;
-  // We only expect one subscription item. 
+  // We only expect one subscription item.
   // If your workflow expects more, you should change this function to handle them.
   if (subscriptionItems.length !== 1) {
     throw new Error(