Introduce a unified model management experience: catalog metadata
validation, vendor management, batch delete with channel/pricing
cleanup, model pricing snapshot editing with optimistic concurrency,
and an upstream ratio-sync flow with price cells. Move configuration
into dedicated pricing config/metadata-sync/vendor-management backend
services and add audit records for model/vendor/pricing mutations.
Rework the models page around vendors and model connections, add
model-pricing and vendor-management dialogs, and replace the shared
Select usages with the Combobox component across subscriptions,
plugins, OAuth presets, audit filters, and settings. Add the model
pricing panel and verify behavior with focused tests.
