fix: offload building DTOs to GUHF

DTO building allows for fully returning correct event's
skills and registrations

WebApp/Mapping/EventSkillMapping.cs

@@ -13,4 +13,12 @@ public static class EventSkillMapping
             SkillId = SSDto.Skill,
         };
     }
+
+    public static SkillSummaryDto ToSkillSummaryDto(this EventSkill es)
+    {
+        return new SkillSummaryDto{
+            SkillId   = es.SkillId,
+            SkillName = es.Skill.Name
+        };
+    }
 }