fix(storefront): BACK-475 Display backorder message on cart page

Add backorder message below quantity controls in cart items when
stock_position.backorder_message is available, with null-safe checks.
Style the message with zero bottom margin for proper alignment.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: bc-apostoliuk

assets/scss/components/stencil/cart/_cart.scss

@@ -227,6 +227,9 @@ $card-preview-zoom-bottom-offset:       6rem;
         }
     }
 
+    .cart-item-backorder-message {
+        margin-bottom: 0;
+    }
 }
 
 .cart-item-label {

lang/en.json

@@ -727,6 +727,8 @@
         "change_product_options": "Change options for {name}",
         "quantity_decrease": "Decrease Quantity of {name}",
         "quantity_increase": "Increase Quantity of {name}",
+        "quantity_backordered": "{quantity} will be backordered",
+        "quantity_on_hand": "{quantity} ready to ship",
         "quantity_error_message":"The quantity should contain only numbers",
         "purchase_units": "{quantity, plural, =0{0 units} one {# unit} other {# units}}",
         "max_purchase_quantity": "Maximum Purchase:",

templates/components/cart/content.html

@@ -137,7 +137,23 @@ <h2 class="cart-item-name">
                             </button>
                         {{/if}}
                     </div>
-
+                    {{#if stock_position}}
+                        {{#if ../cart.inventory_settings.show_quantity_on_hand}}
+                            {{#all stock_position.quantity_on_hand stock_position.backorder_message}}
+                                <p class="cart-item-backorder-message">{{lang 'products.quantity_on_hand' quantity=stock_position.quantity_on_hand}}</p>
+                            {{/all}}
+                        {{/if}}
+                        {{#if ../cart.inventory_settings.show_quantity_on_backorder}}
+                            {{#if stock_position.quantity_backordered}}
+                                <p class="cart-item-backorder-message">{{lang 'products.quantity_backordered' quantity=stock_position.quantity_backordered}}</p>
+                            {{/if}}
+                        {{/if}}
+                        {{#if ../cart.inventory_settings.show_backorder_message}}
+                            {{#if stock_position.backorder_message}}
+                                <p class="cart-item-backorder-message">{{stock_position.backorder_message}}</p>
+                            {{/if}}
+                        {{/if}}
+                    {{/if}}
                 </td>
 
                 <td class="cart-item-block cart-item-info">