test: harden MVP QA gate

.storybook/preview.ts

@@ -1,5 +1,17 @@
 import "../src/app.css";
 import type { Preview } from "@storybook/sveltekit";
+import { setupWorker } from "msw/browser";
+import { externalApiHandlers } from "../src/lib/testing/external-api-mocks";
+
+if (typeof window !== "undefined") {
+  const worker = setupWorker(...externalApiHandlers);
+  void worker.start({
+    onUnhandledRequest: "bypass",
+    serviceWorker: {
+      url: "/mockServiceWorker.js",
+    },
+  });
+}
 
 const preview: Preview = {
   parameters: {