Get agent status and kill-switch state (HMAC or API key)

<!-- relayer:auth-badge:start --> > **Auth: agent HMAC or API key.** Accepts the agent's own HMAC credentials (runtime self-call) **or** the integrator's ApiKey (backend query on the agent's behalf). <!-- relayer:auth-badge:end --> Returns the agent's current lifecycle status and a `killSwitch` boolean (`true` iff status === 'killed'). Polled every 30s by `@relayerfi/agent-sdk` KillSwitch to gate payment operations. Accepts the agent's own HMAC headers or an integrator API key.