Add fully-injected MainWindowViewModel constructor

Introduce an injected constructor taking IHardwareMonitorService, ILogger,
IRemoteWebServer (+ the concrete selection/plot/startup services) and
IStartupTracer, with shared settings initialization. A transitional 2-arg
constructor still builds the legacy graph for MainWindow until it is
DI-resolved; an _ownsServices flag keeps disposal correct across both paths.

Break the VM<->RemoteWebServer construction cycle by moving the root provider
to RemoteWebServer.SetRootProvider (removing it from the constructor), and make
RemoteWebServer.Quit idempotent. Update RemoteWebServer tests for the new ctor.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

LibreHardwareMonitor.Windows.WinUI/Services/IRemoteWebServer.cs

@@ -24,6 +24,8 @@ public interface IRemoteWebServer : IDisposable
 
     string UserName { get; set; }
 
+    void SetRootProvider(Func<ViewModels.SensorTreeItemViewModel?> rootProvider);
+
     void SetPassword(string plainPassword);
 
     bool Start();