Enable or disable a bounded set of slugs

Enables or disables up to 50 slugs (provider ids or provider/endpoint) in one transaction, each with the row semantics of the single write: a provider entry converges its endpoint-level enablement overrides to inherit (and clears their MCP pins when it turns off); an endpoint entry writes its own row (and drops its own pin when it turns off). Markup overrides are preserved. Everything is validated before anything is written; entries apply in the order given; the response reports the effective enablement per entry. Open to personal accounts. Registered ahead of the provider routes, so batch is never read as a provider id.