Refresh the API catalog manifest from GitHub

Rebuilds the internal catalog manifest from the jentic/jentic-public-apis repository. The manifest is used by lazy import — when you POST /credentials for an API not yet in your local registry, Jentic Mini resolves the spec from this manifest automatically.

Fetches the curated apis.json index and the workflows directory listing (two unauthenticated HTTP requests). Safe to call repeatedly. The manifest auto-refreshes daily; only call this explicitly if you need immediate sync after a new API has been added to the public catalog.