style(frontend): move AppShell test imports to top (merge act, add useSessionStore)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/shell/AppShell.session-mgmt.test.tsx

@@ -1,10 +1,11 @@
-import { render, screen, waitFor, within } from "@testing-library/react";
+import { act, render, screen, waitFor, within } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { http, HttpResponse } from "msw";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import { server } from "../test/msw";
 import { FakeEventSource } from "../test/fakeEventSource";
 import { AppShell } from "./AppShell";
+import { useSessionStore } from "../store/sessionStore";
 
 function wrap() {
   const client = new QueryClient({ defaultOptions: { queries: { retry: false } } });
@@ -78,9 +79,6 @@ test("a failed resume keeps the panel open and does not activate the session", a
   await waitFor(() => expect(screen.getByText("Domanda originale")).toBeInTheDocument());
 });
 
-import { act } from "@testing-library/react";
-import { useSessionStore } from "../store/sessionStore";
-
 test("WIP icon toggles the Model activity panel and shows the streamed text", async () => {
   wrap();
   // Activate a session by opening + resuming is heavy; instead drive the store directly.