Streaming sessions can now accept shell commands from the client

In streaming input mode, another program sends messages into a running Claude Code session one after another. That mode used to reject anything that was not one of its accepted kinds, with the error "only prompt commands are supported in streaming mode". The accepted kinds are prompts, orphaned permission requests, task notifications and poll events.

A shell command is now also accepted when the client marks it as a client shell command. Turn details now also carry whether the turn came from an email sender.