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/Usage/TokenTracker/FakeTokenTrackerClient.cs

@@ -38,6 +38,15 @@ public sealed class FakeTokenTrackerClient : ITokenTrackerClient
         return ExportResult;
     }
 
+    public TokenTrackerDashboard DashboardResult { get; set; } = new(true, "http://127.0.0.1:7680/", null);
+    public int DashboardCalls;
+
+    public Task<TokenTrackerDashboard> StartDashboardAsync(CancellationToken ct = default)
+    {
+        Interlocked.Increment(ref DashboardCalls);
+        return Task.FromResult(DashboardResult);
+    }
+
     public Task<TokenTrackerRunResult> InstallAsync(IProgress<string>? output = null, CancellationToken ct = default)
     {
         Interlocked.Increment(ref InstallCalls);

tests/ClaudeDo.Worker.Tests/Usage/TokenTracker/TokenTrackerArgsTests.cs

@@ -39,4 +39,12 @@ public sealed class TokenTrackerArgsTests
     {
         Assert.Equal(new[] { "i", "-g", "tokentracker-cli" }, TokenTrackerArgs.Install());
     }
+
+    [Fact]
+    public void Serve_PinsThePortAndOptsOutOfBrowserAndCloudSync()
+    {
+        Assert.Equal(
+            new[] { "serve", "--port", "7681", "--no-open", "--no-sync" },
+            TokenTrackerArgs.Serve(7681));
+    }
 }

tests/ClaudeDo.Worker.Tests/Usage/TokenTracker/TokenTrackerServiceTests.cs

@@ -13,6 +13,32 @@ public sealed class TokenTrackerServiceTests
         return (new TokenTrackerService(client, new TokenTrackerState(), () => clock), client);
     }
 
+    [Fact]
+    public async Task OpenDashboardAsync_ReturnsTheUrlWhenTheCliIsInstalled()
+    {
+        var (service, client) = Build();
+
+        var dashboard = await service.OpenDashboardAsync();
+
+        Assert.True(dashboard.Ok);
+        Assert.Equal("http://127.0.0.1:7680/", dashboard.Url);
+        Assert.Equal(1, client.DashboardCalls);
+    }
+
+    [Fact]
+    public async Task OpenDashboardAsync_MissingCli_ReportsTheProbeErrorWithoutSpawning()
+    {
+        var (service, client) = Build();
+        client.Probe = new TokenTrackerProbe(false, null, true, "v22.1.0", "'tokentracker' not found on PATH.");
+
+        var dashboard = await service.OpenDashboardAsync();
+
+        Assert.False(dashboard.Ok);
+        Assert.Null(dashboard.Url);
+        Assert.Equal("'tokentracker' not found on PATH.", dashboard.Error);
+        Assert.Equal(0, client.DashboardCalls);
+    }
+
     [Fact]
     public async Task RefreshAsync_StoresParsedExport()
     {