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.

tests/ClaudeDo.Worker.Tests/UiVm/TasksIslandViewModelPlanningTests.cs

@@ -180,6 +180,9 @@ sealed class FakeWorkerClient : IWorkerClient
     public Task<TokenTrackerStatusDto?> RefreshTokenTrackerAsync() => GetTokenTrackerStatusAsync();
 
     public Task<TokenTrackerStatusDto?> InstallTokenTrackerAsync() => GetTokenTrackerStatusAsync();
+
+    public Task<TokenTrackerDashboardDto?> OpenTokenTrackerDashboardAsync() =>
+        Task.FromResult<TokenTrackerDashboardDto?>(new TokenTrackerDashboardDto(false, null, "not configured"));
 }
 
 // ── Helper to build VM with pre-seeded Items ──────────────────────────────────