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/WorkerClient.cs

@@ -698,6 +698,9 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
     public Task<TokenTrackerStatusDto?> InstallTokenTrackerAsync()
         => TryInvokeAsync<TokenTrackerStatusDto>("InstallTokenTracker");
 
+    public Task<TokenTrackerDashboardDto?> OpenTokenTrackerDashboardAsync()
+        => TryInvokeAsync<TokenTrackerDashboardDto>("OpenTokenTrackerDashboard");
+
     // IWorkerClient explicit implementations (drop typed return values)
     async Task IWorkerClient.StartPlanningSessionAsync(string taskId, CancellationToken ct)
         => await StartPlanningSessionAsync(taskId, ct);
@@ -872,6 +875,8 @@ public sealed record TaskUsageRowDto(
     bool? Productive = null,
     bool? OneShot = null);
 
+public sealed record TokenTrackerDashboardDto(bool Ok, string? Url, string? Error);
+
 public sealed record TokenTrackerStatusDto(
     bool Installed,
     string? Version,