feat(grn): add update functionality for draft GRNs and support document-level discounts

- Implemented Update method in GrnsController to allow editing of draft GRNs.
- Enhanced CreateGrnRequest to include an optional totalDiscount property.
- Updated GrnService to handle GRN updates, including validation and line item processing.
- Modified NewGrnPage to support editing existing GRNs and applying document-level discounts.
- Improved UI in NewItemPage and GrnDetailPage for better user experience.
- Added search functionality to Select component for improved item selection.

Frontend/erp-system/components/Layouts/AppSidebar.tsx

@@ -120,7 +120,7 @@ const navItems: {
       // { title: "Reports", code: "sales.reports", href: "/dashboard/sales/reports", icon: FileBarChart },
     ],
   },
-  { title: "Receiving", code: "receiving", href: "/dashboard/receiving/grn", icon: PackageCheck, chevron: true },
+  { title: "GRN", code: "receiving", href: "/dashboard/receiving/grn", icon: PackageCheck, chevron: true },
   {
     title: "Stock",
     code: "stock",