chore: add monitor api route

src/app/api/ping/route.ts

@@ -0,0 +1,9 @@
+import { NextResponse } from 'next/server';
+
+/**
+ * It is used to check if the server is running.
+ * You can use tools like Uptime Kuma to monitor this endpoint.
+ */
+export async function GET() {
+  return NextResponse.json({ message: 'pong' });
+}