Exponential backoff overflow causes multi-day delays at high retry counts

Exponential backoff overflows at retry attempt 20, resulting in delays of 2^20 seconds (approximately 12 days). Tasks with persistent failures accumulate excessive retry delays instead of being marked as permanently failed.

Cap max_delay at 3600 seconds (1 hour) in exponential backoff configuration. Divert tasks exceeding max retry attempts to dead letter queue (DLQ) for manual inspection and permanent failure handling.