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.Worker.Tests/UiVm/TasksIslandViewModelPlanningTests.cs

@@ -126,6 +126,7 @@ sealed class FakeWorkerClient : IWorkerClient
     public Task ClearOnlineInboxAuthAsync() => Task.CompletedTask;
     public Task SendInteractiveMessageAsync(string taskId, string text) => Task.CompletedTask;
     public Task StopInteractiveSessionAsync(string taskId) => Task.CompletedTask;
+    public Task InterruptInteractiveSessionAsync(string taskId) => Task.CompletedTask;
     public IReadOnlyList<ActiveTask> GetActiveTasks() => System.Array.Empty<ActiveTask>();
 }