test(settings): follow the moved pages in e2e and cover the phone navigation

Point the header, overscroll and timezone specs at the pages that hold
those cards now, add the module pages and Preview features to the
one-piece sweep, and add a 390 px journey through the grouped section
sheet. Unit coverage for the Preview features card.

src/components/settings/__tests__/preview-section.test.tsx

@@ -0,0 +1,51 @@
+import { describe, expect, it } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+import { I18nProvider } from "@/lib/i18n/context";
+import { queryKeys } from "@/lib/query-keys";
+import { PreviewSection } from "../preview-section";
+import { primeLocales } from "@/__tests__/helpers/prime-locales";
+
+primeLocales("de");
+
+function render(topics: boolean | undefined, locale: "en" | "de" = "en") {
+  const client = new QueryClient({
+    defaultOptions: { queries: { retry: false, refetchOnMount: false } },
+  });
+  if (topics !== undefined) {
+    client.setQueryData(queryKeys.previewFeatures(), { topics });
+  }
+  return renderToStaticMarkup(
+    <I18nProvider initialLocale={locale}>
+      <QueryClientProvider client={client}>
+        <PreviewSection />
+      </QueryClientProvider>
+    </I18nProvider>,
+  );
+}
+
+describe("<PreviewSection>", () => {
+  it("shows the Topics switch off by default, saved on change", () => {
+    const html = render(false);
+    expect(html).toContain('data-slot="settings-preview-topics-switch"');
+    expect(html).toMatch(
+      /data-slot="settings-preview-topics-switch"[^>]*aria-checked="false"|aria-checked="false"[^>]*data-slot="settings-preview-topics-switch"/,
+    );
+    expect(html).toContain("Topics (beta)");
+    // A switch, no Save: one save model per card.
+    expect(html).not.toContain('type="submit"');
+  });
+
+  it("reads on once the person switched it on", () => {
+    expect(render(true)).toMatch(
+      /data-slot="settings-preview-topics-switch"[^>]*aria-checked="true"|aria-checked="true"[^>]*data-slot="settings-preview-topics-switch"/,
+    );
+  });
+
+  it("says the existing pages stay as they are and nothing raw leaks", () => {
+    const html = render(false, "de");
+    expect(html).toContain("Themen (Beta)");
+    expect(html).not.toContain("settings.preview.");
+  });
+});