Add new Backend structure with proper .NET 8 projects

src/Backend/DiunaBI.Core/Models/Layer.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+
+namespace DiunaBI.Core.Models;
+
+public enum LayerType
+{
+    Import,
+    Processed,
+    Administration,
+    Dictionary,
+}
+public class Layer
+{
+    #region Properties
+    [Key]
+    public Guid Id { get; init; }
+    [Required]
+    public int Number { get; init; }
+    [Required]
+    [MaxLength(50)]
+    public string? Name { get; set; }
+    [Required]
+    public LayerType Type { get; init; }
+    [Required]
+    public DateTime CreatedAt { get; set; }
+    [Required]
+    public DateTime ModifiedAt { get; set; }
+    [Required]
+    public bool IsDeleted { get; init; } = false;
+    [Required]
+    public bool IsCancelled { get; init; } = false;
+    #endregion
+    #region Relations
+    public ICollection<Record>? Records { get; init; }
+    [Required]
+    public Guid CreatedById { get; set; }
+    public User? CreatedBy { get; init; }
+    [Required]
+    public Guid ModifiedById { get; set; }
+    public User? ModifiedBy { get; init; }
+    public Guid? ParentId { get; init; }
+    public Layer? Parent { get; init; }
+    #endregion
+}