feat: add Amvstrm as source for /episodes

Summary:

Test Plan:

src/mocks/anify/episodes.ts

@@ -3,7 +3,7 @@ import { HttpResponse, http } from "msw";
 export function getAnifyEpisodes() {
   return http.get("https://api.anify.tv/episodes/:aniListId", ({ params }) => {
     const aniListId = Number(params["aniListId"]);
-    if (aniListId === 3 || aniListId < 0) {
+    if (aniListId === 3 || aniListId === 4 || aniListId < 0) {
       return HttpResponse.json([]);
     }