Refactor sales pipeline: ShopPO, Invoice, SysConfig models

Major refactor replacing Sale/Order with ShopPO → Invoice → LoadingSheet flow. Removed legacy Sale/Order models and features; introduced ShopPO, ShopPOItem, Invoice, LoadingSheetOrder, and SysConfig models. Updated related entities, enums, repositories, and controllers. Added new migrations for schema changes and system config. Overhauled business logic and DI registrations. Updated documentation with migration plan.

Distribution/Models/LoadingSheetItem.cs

@@ -2,10 +2,8 @@ using System.ComponentModel.DataAnnotations.Schema;
 
 namespace Distribution.Models
 {
-    public class LoadingSheetItem
+    public class LoadingSheetItem : Template
     {
-        public Guid Id { get; set; } = Guid.NewGuid();
-
         public Guid FK_LoadingSheetId { get; set; }
         [ForeignKey("FK_LoadingSheetId")]
         public LoadingSheet LoadingSheet { get; set; }
@@ -14,8 +12,14 @@ namespace Distribution.Models
         [ForeignKey("FK_ItemId")]
         public Item Item { get; set; }
 
+        public Guid FK_WarehouseId { get; set; }
+        [ForeignKey("FK_WarehouseId")]
+        public Warehouse Warehouse { get; set; }
+
+        public Guid? FK_ShopPOItemId { get; set; }
+        [ForeignKey("FK_ShopPOItemId")]
+        public ShopPOItem? ShopPOItem { get; set; }
+
         public decimal QuantityDispatched { get; set; }
-        public decimal? QuantityReceived { get; set; }
-        public decimal? QuantityResolved { get; set; }
     }
 }