Test: Assert the site name sync re-emits exactly once

Review feedback: the positive assertion had no call count, so a second
re-emission would have gone unnoticed. It now uses
toHaveBeenCalledExactlyOnceWith. The negative case keeps not.toHaveBeenCalled,
where a count would not add anything.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: az108

src/test/webapp/app/shared/language/site-name-translation-sync.service.spec.ts

@@ -28,7 +28,7 @@ describe('SiteNameTranslationSync', () => {
     siteConfig.siteName.set('New Portal');
     TestBed.tick();
 
-    expect(setTranslation).toHaveBeenCalledWith('en', {}, true);
+    expect(setTranslation).toHaveBeenCalledExactlyOnceWith('en', {}, true);
   });
 
   it('should do nothing when no language is active yet', () => {