refactor(ui): remove the stale-worker banner

The banner compared the running worker's build SHA against the
selected list's HEAD via a git ancestor check on every list switch
and reconnect. It added a git-rev-parse MSBuild target, a hub call,
and a poll loop for a corner case that hasn't come up in practice —
not worth the moving parts.

tests/ClaudeDo.Ui.Tests/StubWorkerClient.cs

@@ -170,8 +170,6 @@ public abstract class StubWorkerClient : IWorkerClient
     public virtual Task DeleteDailyNoteAsync(string id) => Task.CompletedTask;
     public string LastPrepLog = "";
     public virtual Task<string> GetLastPrepLogAsync() => Task.FromResult(LastPrepLog);
-    public WorkerBuildInfoDto? WorkerBuildInfo;
-    public virtual Task<WorkerBuildInfoDto?> GetWorkerBuildInfoAsync() => Task.FromResult(WorkerBuildInfo);
     public virtual Task RefineTaskAsync(string taskId) => Task.CompletedTask;
 
     public virtual Task<ClaudeBinDto?> GetClaudeBinAsync() => Task.FromResult<ClaudeBinDto?>(null);