feat: DSC enrollment + MFA controls, user CRUD UX, auth error hardening

- DSC module: list/enroll/revoke dialogs and dsc.service (m_bank_user_dsc API)
- Access control: DSC + MFA toggles via disable-confirm-dialog
- Two-factor auth: expanded UX (DSC + OTP flows)
- Users: create/edit form polish, success snackbar on edit, DSC widget
  retained only inside dsc/ (removed from view-user)
- Auth: X-Requested-With added globally; error handler null-safe on
  empty 500 bodies

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/core/authentication/authentication.interceptor.ts

@@ -20,7 +20,10 @@ import { SettingsService } from 'app/settings/settings.service';
 /** Http request (default) options headers. */
 const httpOptions: { headers: { [key: string]: string } } = {
   headers: {
-    'Fineract-Platform-TenantId': environment.fineractPlatformTenantId
+    'Fineract-Platform-TenantId': environment.fineractPlatformTenantId,
+    // Suppresses Spring's WWW-Authenticate: Basic header on 401, which prevents
+    // the browser's native sign-in dialog from hijacking expired-session responses.
+    'X-Requested-With': 'XMLHttpRequest'
   }
 };