feat(mtconnect): host registration + DriverTypeNames const + guard parity (Task 16)

Register the MTConnect factory + probe with the Host, add the
DriverTypeNames.MTConnect constant, and keep DriverTypeNamesGuardTests green.

- DriverTypeNames: new MTConnect const + appended to All.
- DriverFactoryBootstrap: MTConnectDriverFactoryExtensions.Register in
  Register(...) at the default Tier A (managed HttpClient/XML, in-process;
  Tier C is the only tier arming process-recycle, wrong here), and
  TryAddEnumerable(IDriverProbe -> MTConnectDriverProbe) in
  AddOtOpcUaDriverProbes so the probe reaches admin-only nodes (the
  admin-pinned Test-Connect singleton) without double-registering on a
  fused admin,driver node.
- Host.csproj: ProjectReference to Driver.MTConnect (required to compile
  the Register call).
- Core.Abstractions.Tests.csproj: ProjectReference to Driver.MTConnect so
  the guard's bin scan discovers the factory. This and the constant MUST
  land together -- verified RED (2/4 facts) with the constant alone.
- DriverProbeRegistrationTests: MTConnect added to AdminUiDriverTypeKeys;
  its idempotency fact asserts distinct-probe-count and goes RED without
  this (and RED if TryAddEnumerable is downgraded to AddSingleton).

Reconciles all four "MTConnect" literals onto the one constant: the
factory's DriverTypeName, MTConnectDriver.DriverType, and
MTConnectDriverProbe.DriverType now all alias DriverTypeNames.MTConnect
(no circular reference -- Core.Abstractions is a leaf both driver
projects already reference). This is the repo's TwinCat/Focas anti-drift
convention.

tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.csproj

@@ -38,6 +38,7 @@
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Galaxy\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.csproj"/>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Calculation\ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj"/>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Sql\ZB.MOM.WW.OtOpcUa.Driver.Sql.csproj"/>
+        <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.MTConnect\ZB.MOM.WW.OtOpcUa.Driver.MTConnect.csproj"/>
         <!-- Ships no driver factory (it is a historian backend, not an Equipment driver), so the
              DriverTypeNames guard skips it — but it does hard-code OPC UA status constants, which
              puts it in StatusCodeParityTests' scope. -->

tests/Server/ZB.MOM.WW.OtOpcUa.Host.IntegrationTests/DriverProbeRegistrationTests.cs

@@ -32,6 +32,7 @@ public sealed class DriverProbeRegistrationTests
         "OpcUaClient",
         "GalaxyMxGateway",
         "Calculation",           // v3 Batch 2 pseudo-driver; CalculationProbe registered in DriverFactoryBootstrap
+        "MTConnect",             // MTConnectProbe — read-only Agent driver; probe issues a bare GET /probe
     ];
 
     [Fact]