List Model Metadata

Per-model metadata for the dashboard's detail view, from models.dev.

Covers every model models.dev lists under a configured provider, keyed by the instance:model selector the dashboard uses. available is false when enrichment is disabled (models_dev_metadata) or models.dev could not be reached; the response is then empty and the UI falls back to bundled data. Master-key gated: it describes the gateway's configured providers.