refactor: outsource auth function in all routes

frontend/src/routes/login.tsx

@@ -1,7 +1,11 @@
 import { createFileRoute } from "@tanstack/react-router";
 import { LoginCard } from "../components/LoginCard";
+import { checkLogin } from "../utils/api/auth.ts";
 
 export const Route = createFileRoute("/login")({
+  beforeLoad: async () => {
+    await checkLogin();
+  },
   component: RouteComponent,
 });