change user_name still used as login and add display_name for dashboard view instead of username on login

services/__tests__/apiClient.test.ts

@@ -42,7 +42,7 @@ describe('apiClient', () => {
 
   it('sends CSRF token on POST', async () => {
     document.cookie = 'csrftoken=abc123; path=/';
-    const fetchMock = vi.fn().mockResolvedValue(jsonResponse({ id: 1, user_name: 'admin' }));
+    const fetchMock = vi.fn().mockResolvedValue(jsonResponse({ id: 1, user_name: 'admin', display_name: 'admin' }));
     vi.stubGlobal('fetch', fetchMock);
 
     await api.auth.login('admin', 'admin123');