fix: build and test stability for design overhaul

Fixed missing types, import errors, and updated test suites to match the new editorial design. Verified Docker container build.

app/__tests__/not-found.test.tsx

@@ -1,10 +1,23 @@
 import { render, screen } from '@testing-library/react';
 import NotFound from '@/app/not-found';
-import '@testing-library/jest-dom';
+
+// Mock next/navigation
+jest.mock('next/navigation', () => ({
+  useRouter: () => ({
+    back: jest.fn(),
+    push: jest.fn(),
+  }),
+}));
+
+// Mock next-intl
+jest.mock('next-intl', () => ({
+  useLocale: () => 'en',
+  useTranslations: () => (key: string) => key,
+}));
 
 describe('NotFound', () => {
-  it('renders the 404 page', () => {
+  it('renders the 404 page with the new design text', () => {
     render(<NotFound />);
-    expect(screen.getByText("Oops! The page you're looking for doesn't exist.")).toBeInTheDocument();
+    expect(screen.getByText("Lost in the Liquid.")).toBeInTheDocument();
   });
-});
+});