feat(usage): open the TokenTracker dashboard from the usage monitor

The modal deliberately shows only a slice of the analytics; this hands off
to TokenTracker's own local dashboard for the rest. The worker starts
`tokentracker serve` on demand and returns the URL, the UI opens the browser.

Three things the spawn has to get right: port 7680 is not free on Windows
(Delivery Optimization holds [::]:7680) and serve does not fall back, so we
scan 7680-7689 with a dual-stack bind probe; --no-open because the CLI would
open the browser before the server answers; and the child is a cmd.exe shim,
so shutdown kills the process tree. --no-sync keeps our no-cloud-sync rule.

src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs

@@ -210,4 +210,8 @@ public interface IWorkerClient : INotifyPropertyChanged
     Task<TokenTrackerStatusDto?> GetTokenTrackerStatusAsync();
     Task<TokenTrackerStatusDto?> RefreshTokenTrackerAsync();
     Task<TokenTrackerStatusDto?> InstallTokenTrackerAsync();
+
+    /// <summary>Starts TokenTracker's local dashboard on the worker and returns its URL; opening
+    /// the browser is the caller's job.</summary>
+    Task<TokenTrackerDashboardDto?> OpenTokenTrackerDashboardAsync();
 }