Added "Darker" theme to book reader, i.e. the dark theme with gray text to reduce contrast while reading in the dark.

[RPLgrime]

Added

• Added: Book Reader specific theme called 'Darker'.
• Added: New Translation Key for 'theme-darker' in order for UI to translate correctly to users.

Changed

• Changed: Number of Book Reader built-in themes from (4) to (5). The UI array auto-updates the amount of swatches a user can choose from within the Book Reader drawer.

[RPLgrime]

I don't mind changing the descriptor 'Darker', but I thought it would stack decently between 'Dark' and 'Black'.
Below is a screenshot of the Book Reader drawer with extra Color Theme swatch.

[RPLgrime]

I have a large library and Compact Numbers truncates quite a bit for me, so I thought it would be nice to give users a quick toggle to see their data in both ways. I preserved the Kavita intent by defaulting to Compact Numbers = true.

[majora2007]

I took a brief look at this and the color contrast was pretty bad, so much that me merging it opens me to having to fix it, which defeats the purpose.

Instead, I'd be open if you'd want to try and modify the currently open fonts PR and try to extend it for Book reader themes? This way anyone can have any theme they want for the epub reader.