feat(worker): queue interactive messages by default, interrupt opt-in

StreamingClaudeSession now buffers a mid-turn user message in a FIFO queue and
flushes one when the turn's result arrives (no implicit interrupt). InterruptAsync
only writes the control_request (no-op when idle); the resulting turn-end then
flushes any queued message. New InteractiveSessionService.InterruptAsync +
WorkerHub.InterruptInteractiveSession + IWorkerClient.InterruptInteractiveSessionAsync.

tests/ClaudeDo.Ui.Tests/StubWorkerClient.cs

@@ -150,6 +150,12 @@ public abstract class StubWorkerClient : IWorkerClient
         StoppedInteractive.Add(taskId);
         return Task.CompletedTask;
     }
+    public List<string> InterruptedInteractive { get; } = new();
+    public virtual Task InterruptInteractiveSessionAsync(string taskId)
+    {
+        InterruptedInteractive.Add(taskId);
+        return Task.CompletedTask;
+    }
 
     protected void RaisePropertyChanged(string name) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
 }