fix(v3-batch4-wp2): AddReference sink seam for Organizes UNS→Raw (Wave A review M1)

Close the Wave-A M1 gap: the sink surface had no way to wire the mandated
cross-tree Organizes reference from each UNS reference Variable to its backing
Raw node, forcing WP3 to reopen the frozen surface. Add a dedicated
realm-qualified AddReference method instead.

- IOpcUaAddressSpaceSink.AddReference(sourceNodeId, sourceRealm, targetNodeId,
  targetRealm, referenceType="Organizes"): realm-qualified both ends; idempotent;
  a missing endpoint is a logged no-op (never throws) so a mid-rebuild race can't
  fault a deploy. Base-interface capability (no surgical sniff, no transitional
  default — WP3 wires it explicitly per UNS reference variable).
- SdkAddressSpaceSink forwards to the node manager; DeferredAddressSpaceSink
  forwards unconditionally (like EnsureFolder); NullOpcUaAddressSpaceSink no-ops.
- OtOpcUaNodeManager.AddReference: resolve both nodes by full ns-qualified key
  (variable/folder/condition via ResolveNodeState), guard both-exist, then wire
  the edge bidirectionally (forward Organizes on source, inverse on target) with a
  ReferenceExists idempotency guard + ClearChangeMasks on mutated sides. Reference
  type resolved by ResolveReferenceType (Organizes default). Added internal
  GetNodeReferences test/diagnostic accessor.
- Reflection guard: the exhaustive-forwarding test + the realm-discriminator guard
  auto-cover AddReference (it has two AddressSpaceRealm params) — no edit needed.
- New SdkAddressSpaceSinkTests: Organizes UNS→Raw edge created bidirectionally +
  idempotent; missing endpoint is a safe no-op.
- All 15 IOpcUaAddressSpaceSink test doubles gain the AddReference no-op so the
  solution still builds.

Build: dotnet build ZB.MOM.WW.OtOpcUa.slnx = 0 errors.
Tests: Commons.Tests 310/310; OpcUaServer.Tests 337 passed / 4 pre-existing skips.

Claude-Session: https://claude.ai/code/session_01LVneM3eh1UtJxEisFXgmox

tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/DeferredAddressSpaceSinkTests.cs

@@ -249,6 +249,7 @@ public sealed class DeferredAddressSpaceSinkTests
         public void RebuildAddressSpace() => CallQueue.Enqueue("RB");
         /// <inheritdoc />
         public void RaiseNodesAddedModelChange(string affectedNodeId, AddressSpaceRealm realm = AddressSpaceRealm.Uns) => CallQueue.Enqueue($"NA:{affectedNodeId}");
+        public void AddReference(string sourceNodeId, AddressSpaceRealm sourceRealm, string targetNodeId, AddressSpaceRealm targetRealm, string referenceType = "Organizes") { }
     }
 
     private sealed class SurgicalRecordingSink : IOpcUaAddressSpaceSink, ISurgicalAddressSpaceSink
@@ -298,5 +299,6 @@ public sealed class DeferredAddressSpaceSinkTests
         public void RebuildAddressSpace() { }
         /// <inheritdoc />
         public void RaiseNodesAddedModelChange(string affectedNodeId, AddressSpaceRealm realm = AddressSpaceRealm.Uns) { }
+        public void AddReference(string sourceNodeId, AddressSpaceRealm sourceRealm, string targetNodeId, AddressSpaceRealm targetRealm, string referenceType = "Organizes") { }
     }
 }