Show 'Result' block when the AI uses the "done" tool

[dustinlacewell]

When the agent is finished, it uses the done tool but this block is never rendered.

[poteat]

I think this is intended, if I understand correctly. Not all tools result in the AI being prompted again - for example the ask tool leaves the end-user to respond.

[dustinlacewell]

What I mean is that we should capture the fact that the agent output an "Action" with type "done" with a description, and render it as a proper result block.