feat: implement cart icon component with quantity badge and integrate into store header for improved UI

src/app/app.routes.spec.ts

@@ -2,10 +2,13 @@ import { signal } from '@angular/core';
 import { TestBed } from '@angular/core/testing';
 import { provideRouter, Router } from '@angular/router';
 
+import { of } from 'rxjs';
+
 import { App } from './app';
 import { routes } from './app.routes';
 import { Tenant } from './core/services/tenant.interface';
 import { TenantService } from './core/services/tenant.service';
+import { CartService } from './core/services/cart/cart.service';
 
 const tenant: Tenant = {
   id: 1,
@@ -57,6 +60,13 @@ async function renderAppAt(
       {
         provide: TenantService,
         useValue: tenantService
+      },
+      {
+        provide: CartService,
+        useValue: {
+          cart: signal(null).asReadonly(),
+          loadCart: () => of({ id: 1, items: [], subtotal: '0' })
+        }
       }
     ]
   }).compileComponents();