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.

src/ClaudeDo.Worker/Hub/WorkerHub.cs

@@ -581,6 +581,9 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
     public Task StopInteractiveSession(string taskId) =>
         _interactive.StopAsync(taskId, Context.ConnectionAborted);
 
+    public Task InterruptInteractiveSession(string taskId) =>
+        _interactive.InterruptAsync(taskId, Context.ConnectionAborted);
+
     public async Task<DiscardPlanningOutcome> DiscardPlanningSessionAsync(string taskId, bool dequeueQueuedChildren = false)
     {
         var outcome = await _planning.DiscardAsync(taskId, dequeueQueuedChildren, Context.ConnectionAborted);