Migrate to app router (#2254)

app/feed.atom/route.ts

@@ -0,0 +1,11 @@
+import { buildFeed } from "../../lib/helpers/build-feed";
+
+export const dynamic = "force-static";
+
+export const GET = async () => {
+  return new Response(await buildFeed({ type: "atom" }), {
+    headers: {
+      "content-type": "application/atom+xml; charset=utf-8",
+    },
+  });
+};