docs(client): add retry backoff and circuit breaker resilience recommendations (#104)

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Adds client resilience and backoff recommendations.

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All applicable PR CI workflows passed for 5b82a2c.

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Ready for maintainer code review.

[armstrongsam25]

Thanks for contributing. I reviewed the full diff against current main and the LETS constitution.

The entire guide is two bullets, and neither asserted behavior is documented accurately: current LETSClient._request uses capped exponential delays and Retry-After handling, with no full-jitter sampling or circuit-breaker state/threshold. Please describe the implemented RetryPolicy, retryable statuses, request-id/idempotency rules, total deadline and typed failures, with runnable examples or mark unimplemented proposals explicitly. Do not publish full jitter/circuit breakers as current SDK guarantees.

Please expand this into complete, source-backed documentation before merge (constitution XI and XII). This head contains no measurable executable lines, so changed-line coverage is not applicable; that should be recorded explicitly in the PR. No tests or candidate code were executed during this review.

[armstrongsam25]

Closing after source-based triage of head 5b82a2c. The guide lists full jitter and circuit-breaker thresholding without configuration, code, examples or an explicitly scoped proposal. The current client implements bounded exponential delays and Retry-After handling, with neither mechanism. No usable resilience guidance or implemented correction is supplied.

Evidence: implemented retry handling; bounded retry path; entire submitted guide.

Triage criterion: unsupported-completion. Closing this unmerged PR does not close an unfulfilled task, delete the contributor branch, or award bounty points. A distinct substantive revision may be reviewed after reopening.