Fix issue [BS-2522](https://linear.app/affine-design/issue/BS-2522).
### Why make this change?
If the user data contains illegal content, carrying the user data in the system prompt will run the risk of having the account banned.
### What Changed?
- Move the `Context Documents` to the user prompt.
- Add `withPrompt` in `QueryChatHistoriesInput` options.
- Get chat histories without prompt messages.
- Omit document context when saving messages to the `aiSessionMessage` db.