feat(opcua): materialise Equipment-namespace tags in the live rebuild

Add Phase7Applier.MaterialiseEquipmentTags — a sink-based pass (Task-0 decision A) that
ensures each EquipmentTagPlan's Variable (NodeId = FullName) under its existing equipment
folder, nesting any FolderPath as a sub-folder. Wire it into OpcUaPublishActor.HandleRebuild
after the Galaxy pass. Variables start BadWaitingForInitialData; never re-creates equipment
folders (decision #4).

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/OpcUa/OpcUaPublishActor.cs

@@ -230,6 +230,11 @@ public sealed class OpcUaPublishActor : ReceiveActor
             // + Variable node exist so clients can browse them. The Galaxy driver fills values
             // on a future SubscribeBulk pass; until then variables show BadWaitingForInitialData.
             _applier.MaterialiseGalaxyTags(composition);
+            // Equipment-namespace tags get their own pass: ensures each signal's Variable (and any
+            // FolderPath sub-folder) exists under its already-materialised equipment folder so
+            // clients can browse them. Live values arrive in a later milestone; until then the
+            // variables show BadWaitingForInitialData.
+            _applier.MaterialiseEquipmentTags(composition);
 
             OtOpcUaTelemetry.OpcUaSinkWrite.Add(1, new KeyValuePair<string, object?>("kind", "rebuild"));
             _log.Info("OpcUaPublish: applied rebuild (correlation={Correlation}, added={Added}, removed={Removed}, changed={Changed}, rebuild={Rebuild})",