refactor(driver-opcuaclient): extract OpcUaClientDriverOptions to .Contracts

Move OpcUaClientDriverOptions and all companion enums (OpcUaTargetNamespaceKind,
OpcUaSecurityMode, OpcUaSecurityPolicy, OpcUaAuthType) to a new
Driver.OpcUaClient.Contracts sibling project. The options file had no
using directives — all types were defined in the same file — so no
NuGet mirror enum pattern was required.

Convert two doc-comment references:
  <see cref="OpcUaClientDriver.InitializeAsync"/> → <c>OpcUaClientDriver.InitializeAsync</c>
  <see cref="OpcUaClientDriver.ValidateNamespaceKind"/> → <c>OpcUaClientDriver.ValidateNamespaceKind</c>
per the approved decision — no compilable usings were present.

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

ZB.MOM.WW.OtOpcUa.slnx

@@ -37,6 +37,7 @@
     <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj" />
     <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts.csproj" />
     <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.csproj" />
+    <Project Path="src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts.csproj" />
   </Folder>
   <Folder Name="/src/Drivers/Driver CLIs/">
     <Project Path="src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.Cli.Common/ZB.MOM.WW.OtOpcUa.Driver.Cli.Common.csproj" />

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts/OpcUaClientDriverOptions.cs

@@ -23,7 +23,7 @@ public sealed class OpcUaClientDriverOptions
 
     /// <summary>
     ///     Ordered list of candidate endpoint URLs for failover. The driver tries each in
-    ///     order at <see cref="OpcUaClientDriver.InitializeAsync"/> and on session drop;
+    ///     order at <c>OpcUaClientDriver.InitializeAsync</c> and on session drop;
     ///     the first URL that successfully connects wins. Typical use-case: an OPC UA server
     ///     pair running in hot-standby (primary 4840 + backup 4841) where either can serve
     ///     the same address space. Leave unset (or empty) to use <see cref="EndpointUrl"/>
@@ -148,7 +148,7 @@ public sealed class OpcUaClientDriverOptions
     ///         the remote browse path with no UNS conversion.</item>
     ///     </list>
     ///     The driver enforces the choice at startup — see
-    ///     <see cref="OpcUaClientDriver.ValidateNamespaceKind"/> — so a misconfiguration fails
+    ///     <c>OpcUaClientDriver.ValidateNamespaceKind</c> — so a misconfiguration fails
     ///     draft validation rather than surfacing as a runtime surprise.
     /// </summary>
     public OpcUaTargetNamespaceKind TargetNamespaceKind { get; init; } = OpcUaTargetNamespaceKind.Equipment;

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

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    </PropertyGroup>
+    <!-- NO PackageReference. NO ProjectReference. -->
+</Project>

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

@@ -13,6 +13,7 @@
     </PropertyGroup>
 
     <ItemGroup>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Abstractions\ZB.MOM.WW.OtOpcUa.Core.Abstractions.csproj"/>
     </ItemGroup>