New features: cover omission
- Added --no-cover for EPUB2/3, KEPUB/KEPUB3, and PDF to omit existing covers and suppress fallback-cover generation.
- Handles FB2 files with multiple covers; images also used in the body remain ordinary illustrations.
- KFX/AZW8 ignore the flag with a clear warning because Kindle output requires a cover.
Full Changelog: v1.8.0...v1.8.1