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-routing.tsx

@@ -0,0 +1,23 @@
+/**
+ * Mock for next-intl/routing
+ */
+
+export const defineRouting = (config: any) => config;
+
+export const createNavigation = (_routing: any) => ({
+  Link: ({ children, href, ...props }: any) => (
+    <a href={href} {...props}>
+      {children}
+    </a>
+  ),
+  redirect: jest.fn(),
+  usePathname: () => '/en/test',
+  useRouter: () => ({
+    push: jest.fn(),
+    replace: jest.fn(),
+    prefetch: jest.fn(),
+    back: jest.fn(),
+    forward: jest.fn(),
+    refresh: jest.fn(),
+  }),
+});