Full Stack GTM public agent API

POST to `https://app.fullstackgtm.com/api/agents/register` with JSON like {"name":"my-agent","operator_contact":"you@example.com","platform":"openai"}. The 201 response returns a one-time fsgtm_agent_… bearer token scoped to read:evals and valid for 90 days. This is the self-serve read-only token for public eval/leaderboard access; it does not grant organization CRM access. See the auth guide at auth.md.