refactor(driver-modbus): extract ModbusDriverOptions to .Contracts

Move ModbusDriverOptions (and companion option types) to a new
Driver.Modbus.Contracts sibling project. The contracts project
references only Driver.Modbus.Addressing (itself zero-dep and
Admin-safe) because ModbusDriverOptions.Probe/Family/Region
properties use enum types that live there.

Drop 'using ZB.MOM.WW.OtOpcUa.Core.Abstractions' and replace
<see cref="IHostConnectivityProbe"/> with <c>IHostConnectivityProbe</c>
per the approved decision — the using was doc-comment-only.

The runtime Driver.Modbus project gains a ProjectReference back to
.Contracts; the .slnx is updated accordingly.

ZB.MOM.WW.OtOpcUa.slnx

@@ -25,6 +25,7 @@
     <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Client/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Client.csproj" />
     <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ZB.MOM.WW.OtOpcUa.Driver.Modbus.csproj" />
     <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Addressing/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Addressing.csproj" />
+    <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts.csproj" />
     <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/ZB.MOM.WW.OtOpcUa.Driver.S7.csproj" />
     <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip/ZB.MOM.WW.OtOpcUa.Driver.AbCip.csproj" />
     <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.csproj" />

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts/ModbusDriverOptions.cs

@@ -1,5 +1,3 @@
-using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
-
 namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
 
 /// <summary>
@@ -26,7 +24,7 @@ public sealed class ModbusDriverOptions
     ///     is true the driver runs a tick loop that issues a cheap FC03 at register 0 every
     ///     <see cref="ModbusProbeOptions.Interval"/> and raises <c>OnHostStatusChanged</c> on
     ///     Running ↔ Stopped transitions. The Admin UI / OPC UA clients see the state through
-    ///     <see cref="IHostConnectivityProbe"/>.
+    ///     <c>IHostConnectivityProbe</c>.
     /// </summary>
     public ModbusProbeOptions Probe { get; init; } = new();
 

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    </PropertyGroup>
+
+    <!-- ModbusDriverOptions references enums (ModbusFamily, ModbusRegion, ModbusDataType, etc.)
+         that live in the zero-dependency Addressing project. Addressing itself has no deps
+         and was designed for exactly this use — Admin can reference it without transport-layer deps. -->
+    <ItemGroup>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Driver.Modbus.Addressing\ZB.MOM.WW.OtOpcUa.Driver.Modbus.Addressing.csproj"/>
+    </ItemGroup>
+
+</Project>

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ZB.MOM.WW.OtOpcUa.Driver.Modbus.csproj

@@ -15,6 +15,7 @@
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Abstractions\ZB.MOM.WW.OtOpcUa.Core.Abstractions.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core\ZB.MOM.WW.OtOpcUa.Core.csproj"/>
         <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Driver.Modbus.Addressing\ZB.MOM.WW.OtOpcUa.Driver.Modbus.Addressing.csproj"/>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts\ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts.csproj"/>
     </ItemGroup>
 
     <ItemGroup>