Add sales slip document

Backend/ERPCore/Domain/DocumentTypes.cs

@@ -18,4 +18,5 @@ public static class DocumentTypes
     /// <summary>Production run (docs/30 FR-MFG-08) — <c>PRD-2026-00001</c>.</summary>
     public const string Production = "PRD";
     public const string SalesInvoice = "SI";
+    public const string SalesSlip = "SSL";
 }

Backend/ERPCore/Domain/Entities/SalesSlip.cs

@@ -0,0 +1,36 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+public class SalesSlip
+{
+    public int SalesSlipId { get; set; }
+    public string SlipNo { get; set; } = string.Empty;
+    public DateTime SlipDate { get; set; }
+
+    public int CustomerId { get; set; }
+    public Customer? Customer { get; set; }
+
+    public string CustomerSnapshotName { get; set; } = string.Empty;
+    public int WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public int CashierUserId { get; set; }
+    public User? CashierUser { get; set; }
+
+    public SalesSlipStatus Status { get; set; } = SalesSlipStatus.Draft;
+
+    public decimal Subtotal { get; set; }
+    public decimal DiscountTotal { get; set; }
+    public decimal TaxTotal { get; set; }
+    public decimal GrandTotal { get; set; }
+    public decimal PaidAmount { get; set; }
+    public decimal BalanceAmount { get; set; }
+
+    public DateTime CreatedAt { get; set; }
+    public DateTime? UpdatedAt { get; set; }
+
+    public uint RowVersion { get; set; }
+
+    public ICollection<SalesSlipLine> Lines { get; set; } = new List<SalesSlipLine>();
+}

Backend/ERPCore/Domain/Entities/SalesSlipLine.cs

@@ -0,0 +1,35 @@
+namespace ERPCore.Domain.Entities;
+
+public class SalesSlipLine
+{
+    public int SalesSlipLineId { get; set; }
+
+    public int SalesSlipId { get; set; }
+    public SalesSlip? SalesSlip { get; set; }
+
+    public int ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public string Description { get; set; } = string.Empty;
+
+    public decimal Qty { get; set; }
+    public decimal FreeQty { get; set; }
+    public int UomId { get; set; }
+    public Uom? Uom { get; set; }
+    public int WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public decimal UnitPrice { get; set; }
+    public decimal BaseCost { get; set; }
+    public string PriceSource { get; set; } = string.Empty;
+    public decimal DiscountPct { get; set; }
+    public decimal DiscountAmount { get; set; }
+    public decimal NetUnitPrice { get; set; }
+    public decimal LineTotal { get; set; }
+    public decimal TaxPct { get; set; }
+    public decimal TaxAmount { get; set; }
+    public bool IsFreeIssue { get; set; }
+    public int? ParentLineId { get; set; }
+
+    public uint RowVersion { get; set; }
+}

Backend/ERPCore/Domain/Enums/SalesSlipStatus.cs

@@ -0,0 +1,8 @@
+namespace ERPCore.Domain.Enums;
+
+public enum SalesSlipStatus
+{
+    Draft = 1,
+    Posted = 2,
+    Cancelled = 3
+}