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/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));
+    }
 }