feat(uns): carry created id on UnsMutationResult for equipment create

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/UnsMutationResult.cs

@@ -8,4 +8,6 @@ namespace ZB.MOM.WW.OtOpcUa.AdminUI.Uns;
 /// </summary>
 /// <param name="Ok">Whether the mutation was applied.</param>
 /// <param name="Error">The operator-facing failure message, or <c>null</c> on success.</param>
-public readonly record struct UnsMutationResult(bool Ok, string? Error);
+/// <param name="CreatedId">On a successful create, the new entity's system id (e.g. the generated
+/// <c>EQ-…</c> equipment id) so the caller can navigate to it; <c>null</c> for updates/deletes/failures.</param>
+public readonly record struct UnsMutationResult(bool Ok, string? Error, string? CreatedId = null);