fix: 新增预约区域编码唯一性校验

在保存预约区域时，新增对 CustomCode 的唯一性校验，防止插入重复编码，若已存在则抛出异常提示“编码已存在”。

Src/Dlhis.Basic/Appointment/Services/Implements/AppointmentAreaService.cs

@@ -26,6 +26,10 @@ public class AppointmentAreaService : IAppointmentAreaService
     {
         if (!request.Id.HasValue)
         {
+
+            var exists = await _dbContext.Queryable<AppointmentAreaEntity>().Where(x => x.CustomCode == request.CustomCode).AnyAsync();
+            exists.ThrowIfTrue("编码已存在");
+
             var entity = request.Adapt<AppointmentAreaEntity>();
             entity.CustomCode = request.CustomCode;
             entity.Type = request.Type;