fix: enforce stock limits on basket quantities

No stock validation existed in the ordering flow, allowing customers
to order more items than available.

Cap quantity to ``stock_current`` in ``Baskets::getBasketData()`` when
adding to cart. Add ``min=1`` and ``max=stock`` attributes on the
basket quantity input, with JS clamping in the change handler.
Verify stock again in ``Shop\OrderController::store()`` before saving
the order as a race-condition safeguard.

resources/views/Shop/Baskets/basket.blade.php

@@ -53,7 +53,12 @@
 
             $('.basket-quantity').change(function() {
                 var offer_id = $(this).data('id');
-                var quantity = $(this).val();
+                var quantity = parseInt($(this).val()) || 1;
+                var min = parseInt($(this).attr('min')) || 1;
+                var max = parseInt($(this).attr('max'));
+                if (quantity < min) quantity = min;
+                if (max && quantity > max) quantity = max;
+                $(this).val(quantity);
                 var $row = $(this).closest('.row');
                 updateBasket(offer_id, quantity, function() {
                     calculatePrice($row);