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.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDriverFactoryExtensions.cs

@@ -45,13 +45,16 @@ public static class MTConnectDriverFactoryExtensions
     ///     The <c>DriverInstance.DriverType</c> value this factory answers to.
     /// </summary>
     /// <remarks>
-    ///     Kept identical to <see cref="MTConnectDriver.DriverType"/> — the registry key and the
-    ///     instance's self-reported type must agree or the runtime would look the driver up under a
-    ///     name it never registered. Task 16 adds the matching <c>DriverTypeNames.MTConnect</c>
-    ///     constant (the repo's convention is that dispatch maps key off those constants) and wires
-    ///     the Host registration + guard test; this literal is what that constant must equal.
+    ///     <b>Aliased to <see cref="DriverTypeNames.MTConnect"/>, not a literal.</b> The registry key,
+    ///     the instance's self-reported <see cref="MTConnectDriver.DriverType"/>, the probe's
+    ///     <c>DriverType</c>, and the constant every dispatch map keys off are therefore the same
+    ///     symbol — the repo-wide fix for the historical <c>TwinCat</c>/<c>Focas</c> drift, where a
+    ///     driver's own spelling silently diverged from the constant and dispatch maps missed it.
+    ///     Retained as a named const (rather than deleted in favour of the constant) so the existing
+    ///     factory callers and the sibling <c>*DriverFactoryExtensions.DriverTypeName</c> convention
+    ///     keep working; it is now an alias with no independent value.
     /// </remarks>
-    public const string DriverTypeName = "MTConnect";
+    public const string DriverTypeName = DriverTypeNames.MTConnect;
 
     /// <summary>
     ///     Register the MTConnect factory with the driver registry. The optional