fix(frontend): recover startup and discard stale reasoning answers

vocero-frontend/src/App.test.tsx

@@ -43,6 +43,15 @@ afterEach(() => {
 });
 
 describe("React application", () => {
+  it("offers configuration retry without exposing a broken start control", async () => {
+    vi.mocked(fetch).mockRejectedValueOnce(new Error("offline"));
+    const user = userEvent.setup();
+    render(<App />);
+    await screen.findByRole("alert");
+    expect(screen.queryByRole("button", { name: "Iniciar conversación de voz" })).not.toBeInTheDocument();
+    await user.click(screen.getByRole("button", { name: "Reintentar" }));
+    expect(await screen.findByRole("button", { name: "Iniciar conversación de voz" })).toBeEnabled();
+  });
   it("loads the configured theme and persists voice settings across remounts under StrictMode", async () => {
     const user = userEvent.setup();
     const view = render(