Add --transparent option for background-less rendering

[naivecynics]

This pull request introduces a new --transparent (-T) command-line option to enable background-less (transparent) rendering in compatible terminal environments.

Changes Included

• Added transparent_bg flag (activated via -T or --transparent)
• Modified rendering logic to skip background color characters when transparency is enabled
• Updated the help/usage text to include the new --transparent option

This feature is designed to improve visual integration in terminals with custom or image-based backgrounds

[NoamFav]

actually that is super cool :))), would be nice in main