feat: add ItemOverviewDto for enriched item data in items list

feat: implement CustomerDetailPage for detailed customer view and editing

feat: create CustomersPage for listing and managing customers with filters

feat: add ColumnsMenu component for customizable table columns visibility

feat: implement CSV export functionality for data download

feat: add customer code generation logic for unique customer identifiers

Backend/ERPCore/Dtos/Grn/GrnDtos.cs

@@ -22,7 +22,7 @@ public sealed record GrnDto(
 /// <summary>Row shape for <c>GET /grns</c> — line count instead of the lines themselves.</summary>
 public sealed record GrnSummaryDto(
     int GrnId, string DocNo, int? PoId, int VendorId, int WarehouseId, int BranchId, GrnStatus Status,
-    int CreatedBy, DateTime CreatedAt, DateTime? PostedAt, int LineCount,
+    int CreatedBy, DateTime CreatedAt, DateTime? PostedAt, int LineCount, decimal TotalValue,
     int? PurchaseInvoiceId, string? PurchaseInvoiceNo);
 
 public sealed record CreatedLayerDto(

Backend/ERPCore/Dtos/Items/ItemOverviewDtos.cs

@@ -0,0 +1,18 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Items;
+
+/// <summary>
+/// Item row enriched with cross-module aggregates (current FIFO stock value, low-stock
+/// flag, last purchase, trailing-30-day sales) for the Items list page. Deliberately a
+/// separate endpoint from <see cref="ItemListItemDto"/>'s <c>GET /items</c> — that list
+/// also backs the GRN/PO/Requisition/RFQ item pickers, which don't need these aggregates
+/// computed on every keystroke.
+/// </summary>
+public sealed record ItemOverviewDto(
+    int ItemId, string Sku, string Name,
+    int CategoryId, int? SubCategoryId, int? BrandId,
+    EntityStatus Status,
+    decimal StockQty, decimal StockValue, bool IsLowStock,
+    DateTime? LastPurchaseDate, int? LastSupplierId, string? LastSupplierName,
+    decimal SalesQtyLast30Days);