FIX: various issues with llm and triage management

[SamSaffron]

• Fix search API to only include column_names when present to make the API less confusing
• Ensure correct LLM is used in PMs by tracking and preferring the last bot user
• Fix persona_id conversion from string to integer in custom fields
• Add missing test for PM triage with no replies - ensure we don't try to auto title topic
• Ensure bot users are properly added to PMs
• Make title setting optional when replying to posts
• Add ability to control stream_reply behavior

These changes improve reliability and fix edge cases in bot interactions,
particularly in private messages with multiple LLMs and while triaging posts using personas

[nattsw]

Let's give this a goooo 👀

[SamSaffron]

thanks @nattsw I agree though that playground (especially reply_to) is getting a bit out of control complexity wise, may take some time to clean up tomorrow.