Add reasonable defaults for AI web search integration

[preston]

The Brave search token mechanism we are currently trying does seem to work, but quickly exceeds throttling limits for the free tier and throttling is not handled particularly well. This needs further refinement.

[preston]

Brave has been removed, and we are going to change to a user-hosted instance of the SearXNG image instead. Users can decide whether or not to enable web search, as this by definition requires breaking the AI air gap.

[preston]

CC @danielhmendoza01