fix(ai-help): set chatId on user message

[caugner]

Summary

(MP-658, MP-1478)

Problem

When editing a question after it was initially submitted (without reloading the page), submitting the updated question causes a new topic, because the question is missing the chatId reference.

Solution

Make sure that the chatId is set on the question, so that the re-submitted question lands in the same chat.

---

Screenshots

Before

Screen.Recording.2024-09-06.at.14.05.49.mov

After

Screen.Recording.2024-09-06.at.14.04.59.mov

---

How did you test this change?

1. Ran yarn dev locally with Rumba running locally.
2. Opened http://localhost:3000/en-US/plus/ai-help locally.
3. Asked "How to center a div with CSS? Answer in one word." and waited for the response.
4. Edited the question, then resubmitted it.
5. Verified that the edited question remained in the same chat/tree.

[fiji-flo]

👍