Add order invoice fields

Distribution/Models/Order.cs

@@ -1,12 +1,20 @@
-using System.ComponentModel.DataAnnotations.Schema;
+using System.ComponentModel.DataAnnotations.Schema;
 
 namespace Distribution.Models
 {
     public class Order : Template
     {
-        public Guid FK_SaleId { get; set; }
+        public Guid? FK_SaleId { get; set; }
         [ForeignKey("FK_SaleId")]
-        public Sale Sale { get; set; }
+        public Sale? Sale { get; set; }
+
+        public Guid CreatedByUserId { get; set; }
+        [ForeignKey("CreatedByUserId")]
+        public User CreatedByUser { get; set; }
+
+        /// <summary>Set once an Invoice is created for this PO (either mode). No DB-level FK
+        /// constraint — configured explicitly in Fluent API per order_invoice_lifecycle.md.</summary>
+        public Guid? InvoiceId { get; set; }
 
         public DateTime OrderDate { get; set; }
         public Guid FK_StoreId { get; set; }
@@ -16,6 +24,15 @@ namespace Distribution.Models
         public OrderStatus Status { get; set; } = OrderStatus.Pending;
         public DateTime? FulfilledAt { get; set; }
 
+        /// <summary>Null = Shop PO (items editable). Set = Confirmed PO (items locked). Not modeled
+        /// as an explicit field in order_invoice_lifecycle.md's diagram, but required to implement
+        /// its Business Rule 1 (item edits gated on confirmation) independent of Invoice existing —
+        /// Mode B confirms a PO with no Invoice at all.</summary>
+        public DateTime? ConfirmedAt { get; set; }
+        public Guid? ConfirmedByUserId { get; set; }
+        [ForeignKey("ConfirmedByUserId")]
+        public User? ConfirmedByUser { get; set; }
+
         public ICollection<OrderItem> OrderItems { get; set; } = new List<OrderItem>();
     }
 }