Get Agent Models

Return the curated LLM model list per provider.

Shape: {provider: [{"value": model_id, "label": display_name}, ...]}. First-paint fallback for the Deploy form dropdown, before the user enters an API key. Once a key is entered, prefer POST /agents/models/live - that returns the provider's live list including org-enabled models and fine-tunes the curated list can't know about.