feat(back-end and front-end): calculator improvements

backend/src/main/java/com/printcalculator/dto/PrintSettingsDto.java

@@ -7,6 +7,7 @@ public class PrintSettingsDto {
     // Common
     private String material; // e.g. "PLA", "PLA TOUGH", "PETG"
     private String color;    // e.g. "White", "#FFFFFF"
+    private Integer quantity;
     private Long filamentVariantId;
     private Long printerMachineId;
     
@@ -58,6 +59,14 @@ public class PrintSettingsDto {
         this.filamentVariantId = filamentVariantId;
     }
 
+    public Integer getQuantity() {
+        return quantity;
+    }
+
+    public void setQuantity(Integer quantity) {
+        this.quantity = quantity;
+    }
+
     public Long getPrinterMachineId() {
         return printerMachineId;
     }

backend/src/main/java/com/printcalculator/service/quote/QuoteSessionItemService.java

@@ -239,7 +239,7 @@ public class QuoteSessionItemService {
         item.setQuoteSession(session);
         item.setOriginalFilename(originalFilename);
         item.setStoredPath(quoteStorageService.toStoredPath(persistentPath));
-        item.setQuantity(1);
+        item.setQuantity(normalizeQuantity(settings.getQuantity()));
         item.setColorCode(selectedVariant.getColorName());
         item.setFilamentVariant(selectedVariant);
         item.setMaterialCode(selectedVariant.getFilamentMaterialType() != null
@@ -279,4 +279,11 @@ public class QuoteSessionItemService {
         item.setUpdatedAt(OffsetDateTime.now());
         return item;
     }
+
+    private int normalizeQuantity(Integer quantity) {
+        if (quantity == null || quantity < 1) {
+            return 1;
+        }
+        return quantity;
+    }
 }