Clean up domain entities: shared picture value object, lifecycle and ownership interfaces, explicit tables

backend/Core/Musify.Domain/Entities/User.cs

@@ -11,11 +11,9 @@ public class User : IAuditable
     [DatabaseGenerated(DatabaseGeneratedOption.None)]
     public required long Id { get; set; }
 
-    [Required]
     [MaxLength(48)]
     public required string Name { get; set; }
 
-    [Required]
     [MaxLength(48)]
     public required string NormalizedName { get; set; }
 
@@ -28,10 +26,8 @@ public class User : IAuditable
     [MaxLength(2048)]
     public string? ProfilePictureUrl { get; set; }
 
-    [Required]
     public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
 
-    [Required]
     public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
 
     public ICollection<UserHasTrack> UserTracks { get; set; } = new List<UserHasTrack>();