fix(virtualtags): a disabled VirtualTag is no longer deployed or evaluated (lmxopcua#787)

VirtualTag.Enabled was authorable but ignored by both runtime-plan seams.
AddressSpaceComposer.Compose and DeploymentArtifact.BuildEquipmentVirtualTagPlans
now drop disabled rows (byte-parity), so no node is materialised and no
VirtualTagActor is spawned - the same outcome as a disabled scripted alarm.
DraftValidator exempts a disabled VT from VirtualTagNoEffectiveTrigger.
Calculation tags have no Enabled flag, so no equivalent gap. docs/VirtualTags.md updated.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

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

@@ -615,7 +615,10 @@ public static class AddressSpaceComposer
         // DependencyRefs = the distinct ctx.GetTag("…") literals the VirtualTagActor subscribes to.
         // VirtualTag has no FolderPath today → "".
         var scriptsById = resolvedScripts.ToDictionary(s => s.ScriptId, StringComparer.Ordinal);
+        // A disabled VirtualTag (lmxopcua#787) is not part of the runtime plan: no node, no evaluation —
+        // the same as a disabled scripted alarm (which is not materialised). Mirrored by the artifact decode.
         var equipmentVirtualTags = vtags
+            .Where(v => v.Enabled)
             .OrderBy(v => v.EquipmentId, StringComparer.Ordinal)
             .ThenBy(v => v.Name, StringComparer.Ordinal)
             .Select(v =>

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DeploymentArtifact.cs

@@ -1405,6 +1405,10 @@ internal sealed class ParsedDeploymentArtifact : IDisposable
             if (string.IsNullOrWhiteSpace(virtualTagId) || string.IsNullOrWhiteSpace(equipmentId)
                 || string.IsNullOrWhiteSpace(name)) continue;
 
+            // Enabled (lmxopcua#787): a disabled VirtualTag is not deployed or evaluated — byte-parity with
+            // AddressSpaceComposer.Compose's `.Where(v => v.Enabled)`. Absent/non-bool => the entity default (true).
+            if (el.TryGetProperty("Enabled", out var enEl) && enEl.ValueKind == JsonValueKind.False) continue;
+
             var source = scriptId is not null && scriptSourceById.TryGetValue(scriptId, out var src)
                 ? src : string.Empty;