The hive-wide cost estimate on the dashboard's ST4TS tab used a
hard-coded model->price table in hive_stats.rs. Anthropic list pricing
drifts, so move the table to a nix option operators can keep current
without a code change.
- New `services.hyperhive.modelPrices` option: attrset of model-family
short name -> { input, output, cache_read, cache_write } USD per
million tokens. Passed to `hive-c0re serve --model-prices <json>`.
- hive_stats: `Prices` is now public + Deserialize; add `PriceTable`
type and `resolve_prices` (longest case-insensitive substring key
wins) with the old hard-coded table preserved as `builtin_prices`
fallback for any model not covered.
- Coordinator holds the parsed table (hive-c0re-local, not injected
into containers, so not part of HiveEnv); `/api/stats-hive` reads it.
- Docs: dashboard.md ST4TS cost note updated; option self-documents
via nixosOptionsDoc.
Closes#1434
cc8f58fb24