Fetch the live model list from the Copilot /models endpoint and surface
it through /v1/models, replacing the hardcoded github entry so newly
shipped models appear without a code change. Catalog is cached per
credential and the Copilot token is refreshed on 401/403 before retry.
Also raise the connectivity-test budget to max_tokens:16, since Claude on
Copilot emits no choices at max_tokens:1 and produced a false negative.
Co-authored-by: Cursor <cursoragent@cursor.com>
