הורדת hellogrok-cli 0.1.18

Added
- Per-channel upstream failure circuit breaker. Grok Build retries retryable statuses up to 15 times (≈5.5 minutes per turn), so a channel whose relay is down leaves the user stuck in the "retrying" phase until every attempt fails. After 4 consecutive retryable upstream failures (5xx, transport errors, or error-body read failures) the proxy now answers immediately with a non-retryable 503 proxy_circuit_open and X-Should-Retry: false, so the turn fails fast instead of burning the retry budget. A single probe request is allowed through after a 90-second cooldown: success closes the breaker automatically, failure re-arms it. Any non-5xx upstream response (including 429) resets the failure streak, and each channel has an independent breaker. Streaming failures that occur after headers are sent are unaffected. 10→