test: fix Header TDD test to assert css visibility instead of dom unmounting

components/layout/Header.test.tsx

@@ -77,10 +77,11 @@ describe('Header Dropdown Navigation TDD', () => {
       rerender(<Header navLinks={mockNavLinks} />);
     });
 
-    // 6. Assert dropdown is closed (children are not in the document)
+    // 6. Assert dropdown is closed (visually hidden via CSS)
     await waitFor(() => {
-      expect(screen.queryByText('Kabelbau')).toBeNull();
-      expect(screen.queryByText('Bohrtechnik')).toBeNull();
+      const dropdown = screen.getByText('Kabelbau').closest('div[style*="perspective"]');
+      expect(dropdown?.className).toContain('invisible');
+      expect(dropdown?.className).toContain('opacity-0');
     });
   });
 });