fix: redirect to /dashboard if auth user tries to access /login or /signup

apps/web/pages/signup.tsx

@@ -1,5 +1,6 @@
 import { NextPageContext } from "next";
 import Head from "next/head";
+import { getUserFromToken } from "@documenso/lib/server";
 import Signup from "../components/signup";
 
 export default function SignupPage(props: { source: string }) {
@@ -22,6 +23,16 @@ export async function getServerSideProps(context: any) {
       },
     };
 
+  const user = await getUserFromToken(context.req, context.res);
+  if (user)
+    return {
+      redirect: {
+        source: "/signup",
+        destination: "/dashboard",
+        permanent: false,
+      },
+    };
+
   const signupSource: string = context.query["source"];
   return {
     props: {