Update validators to use IsInEnum for Entity property

Refactored DeleteObjectProcedureValidator, InsertObjectProcedureValidator, and UpdateObjectProcedureValidator to use .IsInEnum() for validating the Entity property. This replaces custom or hardcoded checks with enum-based validation, improving consistency, maintainability, and robustness across all validators.

src/ReC.Application/Common/Validations/DeleteObjectProcedureValidator.cs

@@ -7,6 +7,10 @@ public class DeleteObjectProcedureValidator : AbstractValidator<DeleteObjectProc
 {
     public DeleteObjectProcedureValidator()
     {
+        RuleFor(x => x.Entity)
+            .IsInEnum()
+            .WithMessage("ENTITY must be a valid EntityType value.");
+
         RuleFor(x => x.Start)
             .GreaterThan(0)
             .WithMessage("Start GUID/ID must be greater than 0.");