Refresh Catalog

Re-ask every enabled provider what it lists, then take the rest off the catalog.

The whole deployment rather than one provider: a stored price is what puts a model on a tenant's Models page, and a price under a provider nothing here serves cannot be reached by a per-provider refresh. A model list whose provider nothing defines any more, such as a removed config.yml entry, goes too, and is named in orphaned_rosters. Where no provider offers a model, only those lists go and every price stays; with none of them either, the sweep answers 409. Declared before the /{provider} paths to read in the order the surface is used; no method collides in any case.