chore(runtime): warn on missing VirtualTag evaluator; document Stale-recovery VirtualTag behaviour

Log a WARNING on startup when IVirtualTagEvaluator is not registered so a DI misconfig on a
driver-role node is visible in logs instead of silently evaluating all VirtualTags to NoChange.
Add a comment in PushDesiredSubscriptions noting that TryRecoverFromStale does not call this
method, so VirtualTags remain empty after a Stale recovery until the next deployment dispatch
(intentional, consistent with driver recovery).

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

@@ -524,6 +524,11 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers
         // VirtualTagActor per plan and streams their evaluated values back onto the just-rebuilt
         // address space. Runs on BOTH the fresh-apply path (ApplyAndAck) and the bootstrap-restore
         // path (RestoreApplied) because both call this method, so one send covers both.
+        // NOTE: the Stale-recovery path (TryRecoverFromStale) does NOT call PushDesiredSubscriptions,
+        // so — like drivers — VirtualTags remain empty after a Stale recovery until the next
+        // deployment dispatch. This is intentional and consistent with driver recovery: the Stale
+        // path only restores the revision marker + NodeDeploymentState; a subsequent dispatch
+        // (or a redeploy from AdminUI) triggers the full apply + subscribe pass.
         _virtualTagHost?.Tell(new VirtualTagHostActor.ApplyVirtualTags(composition.EquipmentVirtualTags));
         if (composition.EquipmentVirtualTags.Count > 0)
         {