test(host): 2-node integration test harness + consolidate to one ActorSystem (Task 58)

Builds TwoNodeClusterHarness: two in-process Host-equivalent nodes sharing
an in-memory ConfigDb. Forms a 2-member Akka cluster. ClusterFormationTests
proves both nodes see each other as admin+driver role members.

Fixes a real production bug uncovered while wiring the harness — Program.cs
ran two separate ActorSystems (one from AddOtOpcUaCluster.AkkaHostedService
with cluster HOCON, one from Akka.Hosting.AddAkka with bare HOCON). Cluster
singletons landed on the bare ActorSystem and could not actually form a
cluster ("Configuration does not contain `akka.cluster` node").

Consolidation:
- AddOtOpcUaCluster now only binds AkkaClusterOptions + registers IClusterRoleInfo
- New WithOtOpcUaClusterBootstrap pushes embedded HOCON + Remote/Cluster options
  into Akka.Hosting's AkkaConfigurationBuilder
- AkkaHostedService.cs deleted — Akka.Hosting now owns the lifecycle
- Program.cs + harness call WithOtOpcUaClusterBootstrap inside AddAkka

Why not WebApplicationFactory<Program>? Program.cs reads OTOPCUA_ROLES from
process env (shared across in-process WAFs); the harness replays Program.cs's
DI graph from a clean WebApplicationBuilder per node with per-node config
overrides. Same production extensions, isolated config + Kestrel + Akka ports.

Tests: 93 v2 tests pass (was 91 + 2 new cluster formation), 0 skipped.

tests/Server/ZB.MOM.WW.OtOpcUa.Host.IntegrationTests/ZB.MOM.WW.OtOpcUa.Host.IntegrationTests.csproj

@@ -0,0 +1,36 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+    <PropertyGroup>
+        <IsPackable>false</IsPackable>
+        <IsTestProject>true</IsTestProject>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Host.IntegrationTests</RootNamespace>
+        <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="xunit.v3"/>
+        <PackageReference Include="Shouldly"/>
+        <PackageReference Include="Microsoft.NET.Test.Sdk"/>
+        <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing"/>
+        <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory"/>
+        <PackageReference Include="Akka.Hosting"/>
+        <PackageReference Include="xunit.runner.visualstudio">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\..\src\Server\ZB.MOM.WW.OtOpcUa.Host\ZB.MOM.WW.OtOpcUa.Host.csproj"/>
+        <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Cluster\ZB.MOM.WW.OtOpcUa.Cluster.csproj"/>
+        <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Configuration\ZB.MOM.WW.OtOpcUa.Configuration.csproj"/>
+        <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Commons\ZB.MOM.WW.OtOpcUa.Commons.csproj"/>
+        <ProjectReference Include="..\..\..\src\Server\ZB.MOM.WW.OtOpcUa.Security\ZB.MOM.WW.OtOpcUa.Security.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-g94r-2vxg-569j"/>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-h958-fxgg-g7w3"/>
+    </ItemGroup>
+
+</Project>