Auto-summarize session name from conversation content

[djthorpe]

Summary

Automatically generate and update a session's name field by summarizing the conversation content, so sessions have meaningful human-readable names instead of usernames or empty strings.

Requirements

• After a session receives new messages, periodically summarize the conversation into a short descriptive name
• Use an LLM call to generate the summary (could use the same model or a cheaper/faster one)
• Determine when re-summarization is needed:
  • On first user message (initial name)
  • After N new messages since last summarization
  • When topic appears to have shifted significantly
• Run summarization in the background so it doesn't block the chat response
• Store the summary as the session name field
• Should be configurable (enable/disable, model to use for summarization, update frequency)

Motivation

Sessions currently have generic or empty names, making it hard to identify them in session lists. Auto-generated summaries would make the session list much more useful, similar to how ChatGPT names conversations.