docs(extensions): clarify streaming state for sendMessage parameters

[westhood]

Improve clarity of triggerTurn parameter documentation by explicitly explaining what "idle" and "streaming" mean, and when the parameter is ignored.

[github-actions]

Hi @westhood, thanks for your interest in contributing!

We ask new contributors to open an issue first before submitting a PR. This helps us discuss the approach and avoid wasted effort.

Next steps:

1. Open an issue describing what you want to change and why (keep it concise, write in your human voice, AI slop will be closed)
2. Once a maintainer approves with lgtm, you'll be added to the approved contributors list
3. Then you can submit your PR

This PR will be closed automatically. See https://github.com/badlogic/pi-mono/blob/main/CONTRIBUTING.md for more details.