fix(wizard): prevent duplicate device names in the shopping cart

shop/components/order-wizard.tsx

@@ -310,6 +310,17 @@ export function OrderWizard({
   // Product validation errors (requirements and exclusions)
   const productValidationErrors = useMemo(() => {
     const errors: string[] = []
+
+    // Check for duplicate device names
+    const currentName = deviceName.trim() || (editingIdx !== null ? basketItems[editingIdx]?.deviceName : `Kasse ${basketItems.length + 1}`)
+    const isDuplicate = basketItems.some((item, idx) => {
+      if (editingIdx !== null && idx === editingIdx) return false
+      return item.deviceName.toLowerCase().trim() === currentName.toLowerCase().trim()
+    })
+    if (isDuplicate) {
+      errors.push(`Gerätename "${currentName}" existiert bereits im Warenkorb. Bitte einen anderen Namen wählen.`)
+    }
+
     const selectedProductIds: string[] = []
     Object.values(selections).forEach(s => {
       if (s.productIds && s.productIds.length > 0) {
@@ -349,7 +360,7 @@ export function OrderWizard({
     })
 
     return errors
-  }, [selections, products])
+  }, [selections, products, deviceName, basketItems, editingIdx])
 
   const isNextStepDisabled = !allCategoriesFilled || productValidationErrors.length > 0