[CT-89] Retry backoff/jitter configuration isn't documented in the deployment guide

[mftee]

Overview

contract/src/retry.rs implements retry-with-backoff and jitter for Horizon calls (CT-61), but docs/contract-deployment.md — linked from the README as the deployment guide — doesn't appear to document the relevant environment variables or defaults, making it hard for an operator to tune retry behavior for their deployment's latency/throughput needs.

Tasks

• Document the retry/backoff/jitter configuration options, their defaults, and tuning guidance in docs/contract-deployment.md
• Cross-link from retry.rs's module doc comment to the deployment guide section

Acceptance Criteria

• docs/contract-deployment.md documents every retry-related configuration option and its default

Notes for Contributors

Comment below to be assigned.