Adds retry field to workflow steps with exponential/fixed backoff,
jitter, and configurable max attempts. Retry delays are signal-aware
(abort cancels immediately). Abort errors never trigger retries.
- New src/core/retry.ts: withRetry utility with backoff calculation
- Step execution wrapped in retry loop when retry.max > 1
- Retry attempts logged to stderr as [RETRY] messages
- Dry-run renders retry config (attempts, backoff, base delay)
- Comprehensive validation for all retry fields
scottgl
7d6ecec694