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/ViewModels/Modals/UsageMonitorModalViewModel.cs

@@ -68,6 +68,8 @@ public sealed partial class UsageMonitorModalViewModel : ViewModelBase
     [NotifyPropertyChangedFor(nameof(ShowInstallButton))]
     private bool _isInstalling;
 
+    [ObservableProperty] private bool _isOpeningDashboard;
+
     public bool ModelsEmpty => !IsBusy && ModelRows.Count == 0;
     public bool TasksEmpty => !IsBusy && TaskRows.Count == 0;
 
@@ -229,6 +231,35 @@ public sealed partial class UsageMonitorModalViewModel : ViewModelBase
         finally { IsInstalling = false; }
     }
 
+    /// <summary>Hands off to TokenTracker's own dashboard for everything this modal deliberately
+    /// doesn't show. The worker starts the local server (first start takes a few seconds), we only
+    /// open the browser.</summary>
+    [RelayCommand]
+    private async Task OpenDashboard()
+    {
+        IsOpeningDashboard = true;
+        try
+        {
+            var dashboard = await _worker.OpenTokenTrackerDashboardAsync();
+            if (dashboard is not { Ok: true, Url: { Length: > 0 } url })
+            {
+                ErrorReported?.Invoke(Loc.T("vm.usageMonitor.dashboardFailed",
+                    dashboard?.Error ?? Loc.T("vm.usageMonitor.dashboardUnavailable")));
+                return;
+            }
+
+            var (ok, error) = ShellOpen.Url(url);
+            if (!ok)
+                ErrorReported?.Invoke(Loc.T("vm.usageMonitor.dashboardFailed",
+                    error ?? Loc.T("vm.usageMonitor.dashboardUnavailable")));
+        }
+        catch (Exception ex)
+        {
+            ErrorReported?.Invoke(Loc.T("vm.usageMonitor.dashboardFailed", ex.Message));
+        }
+        finally { IsOpeningDashboard = false; }
+    }
+
     private Task SetPreset(int days)
     {
         ApplyPresetRange(days);