feat: support legacy routes

Summary:

Test Plan:

src/index.ts

@@ -23,6 +23,13 @@ app.route(
   "/search",
   await import("~/controllers/search").then((controller) => controller.default),
 );
+// TODO: Remove this route once v2 is ready
+app.route(
+  "/download",
+  await import("~/controllers/episodes/downloadLegacy").then(
+    (controller) => controller.default,
+  ),
+);
 
 // The OpenAPI documentation will be available at /doc
 app.doc("/openapi.json", {