feat(usage): show official API list cost on Token Usage

[Adam-Dalloul]

Token Usage already counts input, output, cache writes, and cache reads. It just never priced them.

This uses the models.dev catalog Codeg already fetches for OpenCode, including cache_read and cache_write, and turns the current range into an API list estimate.

• Muted line under the hero token total: ≈ $12.40 API list. If some models have no published rate, it says how much of the tokens that covers.
• On the By model list, the existing session hint can also show that row's list cost.
• Missing cache rates leave those tokens unpriced instead of pretending they cost the same as fresh input. Subscription plans still bill differently. This is the public list, not remaining quota.

Hover the estimate for the short disclaimer.