Update tests and e2e files to support locale-based routing

- Replaced static paths with dynamic locale subpaths (`/[locale]/*`) in imports, URLs, and assertions across tests.
- Updated `next-intl` mocks for improved compatibility with `locale`-aware components.
- Standardized `page.goto` and navigation tests with `/en` as the base locale for consistency.

frontend/tests/__mocks__/next-intl-navigation.tsx

@@ -0,0 +1,29 @@
+/**
+ * Mock for next-intl/navigation
+ */
+
+// Create shared mock instances that tests can manipulate
+// Note: next-intl's usePathname returns paths WITHOUT locale prefix
+export const mockUsePathname = jest.fn(() => '/');
+export const mockPush = jest.fn();
+export const mockReplace = jest.fn();
+export const mockUseRouter = jest.fn(() => ({
+  push: mockPush,
+  replace: mockReplace,
+  prefetch: jest.fn(),
+  back: jest.fn(),
+  forward: jest.fn(),
+  refresh: jest.fn(),
+}));
+export const mockRedirect = jest.fn();
+
+export const createNavigation = (_routing: any) => ({
+  Link: ({ children, href, ...props }: any) => (
+    <a href={href} {...props}>
+      {children}
+    </a>
+  ),
+  redirect: mockRedirect,
+  usePathname: mockUsePathname,
+  useRouter: mockUseRouter,
+});