Add Auto Tier recommendation to usage notifications

[cwebster-99]

Rather than show a generic "switch to Auto" recommendation at various usage checkpoints, we can recommend the "next best" Auto tier.

Still working on getting the info from the server. Will update issue as I learn more.

[cwebster-99]

We should look for recommended_auto_tier on the Auto responses.

It is advisory: CAPI sets it when the session has used ≥75% of a user's usage credits, and it names only the next-cheaper Auto tier (e.g. "efficiency"). The current session’s tier stays fixed; acting on it means starting a new Auto session with that tier.

Values: intelligence, balance, efficiency