List model catalog

Returns the catalog of supported models, optionally filtered by provider. When gateway_id and registry_id are supplied, the list is narrowed to the models that registry’s credentials can actually use: AWS Bedrock registries are checked against the AWS control plane (on-demand base models and system-defined inference profiles), and every other provider is checked against its authenticated models listing (so org-restricted API keys and Azure deployments are respected). Malformed ids, providers without a listing, and unreachable provider endpoints are ignored and yield the full catalog.