- Refactored ImageDownloader to use persistent session pattern
- Changed default timeout from 60s to 30s to match test expectations
- Added session management with context manager protocol
- Fixed _get_session() to handle both real and mock sessions
- Fixed download_all_media() to return None for missing URLs
Test fixes:
- Updated all test mocks to use proper async context manager protocol
- Fixed validate_image tests to use public API instead of non-existent private method
- Updated test fixture to use smaller min_file_size for test images
- Fixed retry tests to use proper aiohttp.ClientResponseError with RequestInfo
- Corrected test assertions to match actual behavior (404 returns False, not exception)
All 20 ImageDownloader unit tests now passing (100%)