Show estimated per-model cost in ucode usage

[andy-xu-db]

Adds an estimated USD cost per model to ucode usage, aggregated by model over the last 7 days.

• Prices are fetched live at runtime from the AI Gateway ListExternalProviderModels API — not hardcoded in the package, so new models are priced automatically and there's no static table to maintain.
• Estimates cost as tokens × price, pricing uncached input, cache reads, and output at their own rates.
• Replaces the per-day tool table with a per-model weekly rollup: Model · Requests · Input (incl. cache) · Output · Cost (USD), plus per-tool totals.
• Merges the same model's id/display spellings into one row; models the catalog doesn't cover show no dollar figure.

Cost is an estimate (list price × tokens); no API exposes per-model billed spend.