Add download retry logic tests (12 tests, all passing)
✅ COMPLETE: 12/12 tests passing
Test Coverage:
- Automatic retry: Single item retry, retry all failed items
- Retry count tracking: Count increments on retry, persists across retries
- Maximum retry limit: Items not retried after max, mixed eligibility, configurable max_retries
- Retry state management: Error cleared, progress cleared, status updated, selective retry by IDs
- Exponential backoff: ImageDownloader implements exponential backoff (0.1s→0.2s delays)
All download retry mechanisms validated with proper state management and limit enforcement.
Lukas
9157c4b274