Add runtime address space rebuild integration tests

Tests verify nodes can be added/removed from the OPC UA server at
runtime by mutating FakeGalaxyRepository and triggering a rebuild.
Uses real OPC UA client sessions to browse, subscribe, and observe
changes.

Tests cover:
- Browse initial hierarchy via OPC UA client
- Add object at runtime → new node appears on browse
- Remove object → node disappears from browse
- Subscribe to node, then remove it → publishes Bad quality
- Surviving nodes still browsable after partial rebuild
- Add/remove individual attributes at runtime

Infrastructure:
- OpcUaTestClient helper for programmatic OPC UA client connections
- OpcUaServerFixture updated with GalaxyRepository/MxProxy accessors
- OpcUaService.TriggerRebuild() exposed for test-driven rebuilds
- Namespace index resolved dynamically via session namespace table

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/ZB.MOM.WW.LmxOpcUa.Tests/ZB.MOM.WW.LmxOpcUa.Tests.csproj

@@ -22,6 +22,7 @@
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="6.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="6.0.0" />
     <PackageReference Include="OPCFoundation.NetStandard.Opc.Ua.Server" Version="1.5.374.126" />
+    <PackageReference Include="OPCFoundation.NetStandard.Opc.Ua.Client" Version="1.5.374.126" />
   </ItemGroup>
 
   <ItemGroup>