chore: scaffold .NET solution structure for Phase 6

Creates the four-project .NET 10 solution (ZB.MOM.NatsNet.slnx):
- ZB.MOM.NatsNet.Server: main library with MEL, BCrypt.Net-Next, IronSnappy
- ZB.MOM.NatsNet.Server.Host: console host with Serilog + Microsoft.Extensions.Hosting
- ZB.MOM.NatsNet.Server.Tests: xUnit 2.9 / Shouldly / NSubstitute / BenchmarkDotNet
- ZB.MOM.NatsNet.Server.IntegrationTests: same test stack, separate project

Also adds Phase 6 porting plan and task-tracking JSON.

dotnet/tests/ZB.MOM.NatsNet.Server.Tests/ZB.MOM.NatsNet.Server.Tests.csproj

@@ -0,0 +1,29 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <LangVersion>latest</LangVersion>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="../../src/ZB.MOM.NatsNet.Server/ZB.MOM.NatsNet.Server.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+    <PackageReference Include="Shouldly" Version="*" />
+    <PackageReference Include="NSubstitute" Version="*" />
+    <PackageReference Include="BenchmarkDotNet" Version="*" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+</Project>