Adds a faros callback that batches successful LLM requests and upserts
them into a Faros graph as canonical vcs_UserToolUsage records (with
backing vcs_UserTool and vcs_User records) via the Faros GraphQL API,
the same write path Faros' own first-party usage trackers use. User
identity resolves from key user email, then key user id, then the
request user param; the proxy admin placeholder id is ignored so master
key traffic attributes to the explicit user param.
https://claude.ai/code/session_01S79266vJDYzh7ay3nQ9ENW