Add POI feature and imporve the overall backend implementation

frontend/src/components/domain/unified-wizard/wizards/SalesEntryWizard.tsx

@@ -720,6 +720,7 @@ const ReviewStep: React.FC<EntryMethodStepProps> = ({ data, onComplete }) => {
         // Create individual sales records for each item
         for (const item of data.salesItems) {
           const salesData = {
+            inventory_product_id: item.productId || null, // Include inventory product ID for stock tracking
             product_name: item.product,
             product_category: 'general', // Could be enhanced with category selection
             quantity_sold: item.quantity,