Add pricing and supplier master data

Distribution/Models/PriceList.cs

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+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class PriceList : Template
+    {
+        public string Name { get; set; }
+
+        public Guid? FK_RegionId { get; set; }
+        [ForeignKey("FK_RegionId")]
+        public Region? Region { get; set; }
+
+        public DateTime EffectiveFrom { get; set; }
+        public DateTime EffectiveTo { get; set; }
+
+        public ICollection<PriceListItem> Items { get; set; } = [];
+    }
+}

Distribution/Models/PriceListItem.cs

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+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Distribution.Models
+{
+    public class PriceListItem : Template
+    {
+        public Guid FK_PriceListId { get; set; }
+        [ForeignKey("FK_PriceListId")]
+        public PriceList PriceList { get; set; }
+
+        public Guid FK_ItemId { get; set; }
+        [ForeignKey("FK_ItemId")]
+        public Item Item { get; set; }
+
+        public decimal Price { get; set; }
+
+        /// <summary>
+        /// Floor price for negotiation. Null = no negotiation allowed, Price is fixed.
+        /// Must be less than or equal to Price when set.
+        /// </summary>
+        public decimal? MinPrice { get; set; }
+    }
+}

Distribution/Models/Supplier.cs

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+namespace Distribution.Models
+{
+    public class Supplier : Template
+    {
+        public string Name { get; set; }
+        public string? ContactInfo { get; set; }
+        public decimal? PerformanceScore { get; set; }
+    }
+}
+
+