view(Purchase): Set price automatically based on product.

tienda_ilusion/don_confiao/frontend/don-confiao/src/components/Purchase.vue

@@ -45,6 +45,7 @@
               <v-select
                 v-model="line.product"
                 :items="products"
+                @update:modelValue="onProductChange(index)"
                 item-title="name"
                 item-value="id"
                 label="Producto"
@@ -138,6 +139,11 @@
       },
     },
     methods: {
+      onProductChange(index) {
+        const selectedProductId = this.purchase.saleline_set[index].product;
+        const selectedProduct = this.products.find(p => p.id == selectedProductId);
+        this.purchase.saleline_set[index].unit_price = selectedProduct.price;
+      },
       fetchClients() {
         fetch('/don_confiao/api/customers/')
           .then(response => response.json())