- Add app/utils/retry.py with configurable async retry decorator
- Update DeliveryLog model to track attempt_count and latency_seconds
- Apply @http_retry to engine._exec_forward and _exec_notify methods
- Update save_logs to record retry metadata
- Add comprehensive unit tests for retry functionality
- Support configuration via environment variables (RETRY_*)
This improves reliability for downstream HTTP calls by automatically
retrying transient failures with exponential backoff and jitter.
