Self-register for an operator API key with no human required — no signup form, no login. Use this if you don't already have an api_key from a human operator. Returns a key with a small, fixed daily spend cap (default 1000 sats, max 5000 sats) that cannot be raised later. This key has no free call — purchases are paid over Lightning. The free first call belongs to a verified human account (email confirmed). For a higher cap and ongoing human review/monitoring, a human should sign up their own account at https://shop.getnoden.com/signup instead.