Update agent SQL scope

Restricts which part of the warehouse the AI agent may read via raw SQL.

Null (or an empty schemas list) means unrestricted — the agent can reach anything the project's warehouse connection can reach, which is the behaviour for every project that has not configured a scope.

This is a correctness control rather than a security boundary: raw SQL already requires manage SqlRunner, so the same data is reachable through the SQL Runner regardless. It exists so an agent can be kept off schemas a customer knows are wrong to answer from, such as a retired dbt project living in the same catalog as the current one.