feat: inject ThemeService into App component and enhance responsive styles for navigation items

frontend/src/app/app.ts

@@ -7,6 +7,7 @@ import { BrandMark } from './components/brand-mark';
 import { SignInPage } from './components/sign-in-page/sign-in-page';
 import { WorkspaceNavigation } from './components/workspace-navigation/workspace-navigation';
 import { SessionService } from './services/session.service';
+import { ThemeService } from './services/theme.service';
 
 @Component({
   selector: 'app-root',
@@ -24,6 +25,7 @@ import { SessionService } from './services/session.service';
 })
 export class App implements OnInit {
   readonly session = inject(SessionService);
+  readonly theme = inject(ThemeService);
   readonly userInitial = computed(() => this.session.username().charAt(0).toUpperCase());
 
   ngOnInit() {