fix(opcua): equipment-tag planner diff + folder-scoped NodeIds (review findings)

Two bundle-review fixes + idempotency coverage:
- CRITICAL: the planner ignored EquipmentTags, so an incremental deploy changing only
  equipment tags produced an empty plan and HandleRebuild short-circuited before
  materialising them. Add TagId to EquipmentTagPlan + Added/Removed/ChangedEquipmentTags
  to Phase7Plan (diffed by TagId, in IsEmpty, driving Apply's needsRebuild) — mirroring
  the GalaxyTags treatment.
- IMPORTANT: equipment variable NodeId was the raw driver FullName, which collides across
  identical machines (e.g. two PLCs both exposing register 40001) — the second variable
  was silently dropped. NodeId is now folder-scoped (parent/Name); FullName stays on
  EquipmentTagPlan for the later values-routing milestone.
- Task 4: SDK-backed idempotency test (double-apply -> single variable); restart-safety
  confirmed (RestoreApplied reuses the same RebuildAddressSpace -> HandleRebuild path).
- Minor: align composer equipment-tag sort with the artifact decoder (coalesce FolderPath).

src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Composer.cs

@@ -81,14 +81,18 @@ public sealed record GalaxyTagPlan(
 
 /// <summary>
 ///     One Equipment-namespace tag from a <see cref="Tag"/> row whose <see cref="Tag.EquipmentId"/>
-///     is non-null and whose owning driver's namespace is <c>Equipment</c>-kind. Carries the parent
-///     <see cref="EquipmentId"/> folder (already materialised by <c>Phase7Applier.MaterialiseHierarchy</c>)
-///     the variable hangs under, the optional <see cref="FolderPath"/> sub-folder, the leaf
-///     <see cref="Name"/> display, the OPC UA <see cref="DataType"/>, and the driver-side
-///     <see cref="FullName"/> reference (extracted from <c>Tag.TagConfig</c>) used as the variable
-///     NodeId + read/write routing key. The equipment-signal analogue of <see cref="GalaxyTagPlan"/>.
+///     is non-null and whose owning driver's namespace is <c>Equipment</c>-kind. Carries the stable
+///     <see cref="TagId"/> (diff identity), the parent <see cref="EquipmentId"/> folder (already
+///     materialised by <c>Phase7Applier.MaterialiseHierarchy</c>) the variable hangs under, the
+///     optional <see cref="FolderPath"/> sub-folder, the leaf <see cref="Name"/> display, the OPC UA
+///     <see cref="DataType"/>, and the driver-side <see cref="FullName"/> reference (extracted from
+///     <c>Tag.TagConfig</c>) the later values milestone routes reads/writes by. The variable's NodeId
+///     is folder-scoped (<c>parent/Name</c>), NOT <see cref="FullName"/>, because a raw driver ref
+///     (e.g. a Modbus register) is not unique across identical machines. The equipment-signal
+///     analogue of <see cref="GalaxyTagPlan"/>.
 /// </summary>
 public sealed record EquipmentTagPlan(
+    string TagId,
     string EquipmentId,
     string DriverInstanceId,
     string FolderPath,
@@ -218,9 +222,10 @@ public static class Phase7Composer
                         && namespacesById.TryGetValue(di.NamespaceId, out var ns)
                         && ns.Kind == NamespaceKind.Equipment)
             .OrderBy(t => t.EquipmentId, StringComparer.Ordinal)
-            .ThenBy(t => t.FolderPath, StringComparer.Ordinal)
+            .ThenBy(t => t.FolderPath ?? string.Empty, StringComparer.Ordinal) // coalesce so the sort matches the artifact-decode side exactly
             .ThenBy(t => t.Name, StringComparer.Ordinal)
             .Select(t => new EquipmentTagPlan(
+                TagId: t.TagId,
                 EquipmentId: t.EquipmentId!,
                 DriverInstanceId: t.DriverInstanceId,
                 FolderPath: t.FolderPath ?? string.Empty,