changed shipment_id to integers

backend/app/routers/shipment.py

@@ -44,9 +44,7 @@ async def create_shipment(shipment: ShipmentCreate, db: Session = Depends(get_db
     if not (contact_person or return_address or proposal):
         raise HTTPException(status_code=404, detail="Associated entity not found")
 
-    shipment_id = f'SHIP-{uuid.uuid4().hex[:8].upper()}'
     db_shipment = ShipmentModel(
-        shipment_id=shipment_id,
         shipment_name=shipment.shipment_name,
         shipment_date=shipment.shipment_date,
         shipment_status=shipment.shipment_status,