Add sales invoice document

Backend/ERPCore/Domain/DocumentTypes.cs

@@ -17,4 +17,5 @@ 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";
 }

Backend/ERPCore/Domain/Entities/SalesInvoice.cs

@@ -0,0 +1,41 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+public class SalesInvoice
+{
+    public int SalesInvoiceId { get; set; }
+    public string InvoiceNo { get; set; } = string.Empty;
+    public DateTime InvoiceDate { get; set; }
+
+    public int CustomerId { get; set; }
+    public Customer? Customer { get; set; }
+
+    public string CustomerSnapshotName { get; set; } = string.Empty;
+    public string? CustomerSnapshotTaxNo { get; set; }
+
+    public int WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public SalesInvoiceType InvoiceType { get; set; } = SalesInvoiceType.B2C;
+    public SalesInvoiceStatus Status { get; set; } = SalesInvoiceStatus.Draft;
+
+    public decimal Subtotal { get; set; }
+    public decimal DiscountTotal { get; set; }
+    public decimal TaxTotal { get; set; }
+    public decimal GrandTotal { get; set; }
+    public decimal RoundOff { get; set; }
+    public decimal NetPayable { get; set; }
+    public decimal PaidAmount { get; set; }
+    public decimal BalanceAmount { get; set; }
+
+    public int CreatedBy { get; set; }
+    public User? Creator { get; set; }
+
+    public DateTime CreatedAt { get; set; }
+    public DateTime? UpdatedAt { get; set; }
+
+    public uint RowVersion { get; set; }
+
+    public ICollection<SalesInvoiceLine> Lines { get; set; } = new List<SalesInvoiceLine>();
+}

Backend/ERPCore/Domain/Entities/SalesInvoiceLine.cs

@@ -0,0 +1,35 @@
+namespace ERPCore.Domain.Entities;
+
+public class SalesInvoiceLine
+{
+    public int SalesInvoiceLineId { get; set; }
+
+    public int SalesInvoiceId { get; set; }
+    public SalesInvoice? SalesInvoice { 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/SalesInvoiceStatus.cs

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

Backend/ERPCore/Domain/Enums/SalesInvoiceType.cs

@@ -0,0 +1,9 @@
+namespace ERPCore.Domain.Enums;
+
+public enum SalesInvoiceType
+{
+    B2B = 1,
+    B2C = 2,
+    Cash = 3,
+    Credit = 4
+}