feat: implement unified login flow with LoginButton and contextual LoginDialog for unauthenticated form access

app/form/client.tsx

@@ -17,7 +17,7 @@ import { AlertDialog, AlertDialogAction, AlertDialogCancel, AlertDialogContent,
 import { toast } from "sonner";
 import { submitForm, deleteOwnSubmission } from "@/app/actions/submissions";
 import { Loader2, LogOut } from "lucide-react";
-import { signOut } from "next-auth/react";
+import { signIn, signOut } from "next-auth/react";
 import Image from "next/image";
 import { z } from "zod";
 import { useForm, Controller } from "react-hook-form";
@@ -49,6 +49,14 @@ export function FormLayoutClient({
   );
 }
 
+export function LoginButton() {
+  return (
+    <Button variant="outline" size="sm" onClick={() => signIn("discord", { callbackUrl: window.location.href })}>
+      Login
+    </Button>
+  );
+}
+
 interface Question {
   id: string;
   formId: string;