Add conditional MSW browser worker startup for E2E testing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main.ts

@@ -98,4 +98,14 @@ app.component("ContextMenu", ContextMenu);
 app.component("Draggable", draggable); // Drag and drop
 app.directive("tooltip", Tooltip);
 
-app.mount("#app");
+/**
+ * Starts the MSW service worker when VITE_MSW is set.
+ * Used for E2E testing with mock API responses.
+ */
+async function enableMocking() {
+  if (import.meta.env.VITE_MSW !== "true") return;
+  const { worker } = await import("./mocks/browser.js");
+  await worker.start({ onUnhandledRequest: "bypass" });
+}
+
+enableMocking().then(() => app.mount("#app"));