feat(validation): require TagConfig.FullName on Galaxy alias tags; reframe Tag doc

src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Entities/Tag.cs

@@ -3,9 +3,11 @@ using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
 namespace ZB.MOM.WW.OtOpcUa.Configuration.Entities;
 
 /// <summary>
-///     One canonical tag (signal) in a cluster's generation. Per decision #110:
-///     <see cref="EquipmentId"/> is REQUIRED when the driver is in an Equipment-kind namespace
-///     and NULL when in SystemPlatform-kind namespace (Galaxy hierarchy preserved).
+///     One canonical tag (signal) in a cluster's generation. <see cref="EquipmentId"/> set ⟺ the
+///     tag participates in the Equipment tree, regardless of the driver's namespace kind. A
+///     <c>GalaxyMxGateway</c>-bound equipment tag is an <em>alias</em> — a Galaxy attribute surfaced
+///     under a UNS name, with its Galaxy reference carried in <c>TagConfig.FullName</c>.
+///     <see cref="EquipmentId"/> is NULL for SystemPlatform mirror tags (FolderPath-scoped).
 /// </summary>
 public sealed class Tag
 {
@@ -30,8 +32,8 @@ public sealed class Tag
     public string? DeviceId { get; set; }
 
     /// <summary>
-    ///     Required when driver is in Equipment-kind namespace; NULL when in SystemPlatform-kind.
-    ///     Cross-table invariant enforced by sp_ValidateDraft (decision #110).
+    ///     Set when the tag belongs to an Equipment (driver tag OR Galaxy alias); NULL for
+    ///     SystemPlatform mirror tags.
     /// </summary>
     public string? EquipmentId { get; set; }