[UX] Display spinner immediate after tool completed

> Sluggishness. There is always a long delay (1-2 seconds) between "Completed in XYZ seconds" and the "Thinking" spinner. It makes Q feel sluggish. Can you reduce the perceived gap by eliminating whatever it's going in that time or at least print "thinking'" right away after "Completed"?

https://amzn-aws.slack.com/archives/C064EVBE0LR/p1746716811774539