feat: enhance checkout process with purchase editing and status handling

- Implemented purchase editing functionality in CheckoutPageComponent, allowing users to modify items in their purchase.
- Added a new guard (checkoutPendingPurchaseGuard) to prevent navigation away from the checkout page while a purchase is in progress.
- Updated the login page to handle return URLs after authentication.
- Enhanced product detail page to support direct purchases with a new buyNow method.
- Introduced new UI elements and logic to handle purchase status, including expired and rejected states in PurchaseStatusPageComponent.
- Improved cart component to allow editing of item quantities with a toggle button.
- Added quantity selector enhancements to disable controls when necessary.
- Updated tests to cover new functionalities and ensure proper behavior of components.

src/app/shared/components/cart/cart.component.scss

@@ -21,6 +21,17 @@
   color: #a0a0a0;
 }
 
+.cart-header-actions {
+  gap: 14px;
+}
+
+.cart-edit-btn {
+  color: var(--bs-primary);
+  font-size: 11px;
+  font-weight: 500;
+  text-decoration: none;
+}
+
 .cart-items-container {
   min-height: 0;
   gap: 0;