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

src/app/shared/components/cart-icon/cart-icon.component.html

@@ -0,0 +1,13 @@
+<button
+  type="button"
+  [disabled]="disabled()"
+  [attr.aria-label]="ariaLabel()"
+  class="cart-icon"
+>
+  <div class="cart-icon__container">
+    <i class="fa-solid fa-cart-shopping cart-icon__glyph" aria-hidden="true"></i>
+    @if (hasQuantity()) {
+      <span class="cart-icon__badge" data-testid="cart-badge">{{ quantity() }}</span>
+    }
+  </div>
+</button>