feat(ui): worker client surface for in-app interactive sessions

Adds SendInteractiveMessageAsync/StopInteractiveSessionAsync and the
InteractiveSessionStarted/Ended events to IWorkerClient + WorkerClient
(UI-thread dispatch mirroring TaskQuestionAsked). Updates the IWorkerClient
fakes in both test projects.

src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs

@@ -25,6 +25,9 @@ public interface IWorkerClient : INotifyPropertyChanged
     /// <summary>A pending question was answered, timed out, or the run ended: (taskId, questionId).</summary>
     event Action<string, string>? TaskQuestionResolvedEvent;
 
+    event Action<string>? InteractiveSessionStartedEvent;
+    event Action<string>? InteractiveSessionEndedEvent;
+
     event Action? PrepStartedEvent;
     event Action<string>? PrepLineEvent;
     event Action<bool>? PrepFinishedEvent;
@@ -46,6 +49,8 @@ public interface IWorkerClient : INotifyPropertyChanged
     Task ContinueTaskAsync(string taskId, string followUpPrompt);
     /// <summary>Answer a question a running task raised via AskUser.</summary>
     Task AnswerTaskQuestionAsync(string taskId, string questionId, string answer);
+    Task SendInteractiveMessageAsync(string taskId, string text);
+    Task StopInteractiveSessionAsync(string taskId);
     /// <summary>The question a running task is currently blocked on, if any (for re-attach).</summary>
     Task<PendingQuestionDto?> GetPendingQuestionAsync(string taskId);
     Task ResetTaskAsync(string taskId);