add-pricing-field

Wire a new model-pricing field (a datasheet cost key like cost_per_request, output_cost_per_video_per_second_720p, etc.) end-to-end through Bifrost's pricing engine — Options struct, DB table + migration, datasheet sync upsert columns, cost calculation, custom pricing overrides, public API, OpenAPI docs, MDX docs, and the UI override form. Ends with a repo-wide probe to confirm nothing was missed. Invoked with…