Dev CI red on 8f70bcbd9: UiSmokeWpf lock file and two live test classes that do not skip #5755

Claude posting for Erik Darling.

The Build and WPF smoke checks fail on dev at 8f70bcbd9, and on every PR that merges dev.

Why. #5747 added tools/ui-smoke-wpf/UiSmokeWpf.csproj, whose packages.lock.json pins xunit.v3 at 4.0.1. #5746 then raised xunit.v3 to 4.0.2 in Directory.Packages.props. Its lock-file updates were made before #5747 merged, so they did not include the new project. Locked restore now fails:

tools/ui-smoke-wpf/UiSmokeWpf.csproj : error NU1004: The package reference xunit.v3 version has changed from [4.0.1, ) to [4.0.2, ).

Fix. Regenerate tools/ui-smoke-wpf/packages.lock.json with dotnet restore PerformanceMonitor.sln --force-evaluate and commit it, plus any other lock file that restore rewrites.

A second failure on the same dev commit. The Darling whole-tree guards job fails 34 tests: every test in ExternalAlertDrainLiveTests (21) and ExternalAlertDrainLifecycleLiveTests (13), both added by #5726. Each throws System.ArgumentNullException : Value cannot be null. (Parameter 'Host'). That job runs with no DARLING_TEST_PG, and these two classes do not skip when it is unset, as the other live classes do. The fix adds the same skip, and the PR for this issue carries both fixes, since each one alone would still fail on the other.

Done when Build, WPF smoke and Darling whole-tree guards pass on dev.