Improve epub layout on smartphone

[blackdetail]

Text is shown only on a small portion of screen. I think it is better to show more text on a screen. Please see screenshots for comparison.

[richardr1126]

@blackdetail I will bring this in the next version. Another thing that was overlooked. But v1.1.0 will add custom nav controls in a new header and also includes word-by-word highlighting generated by whisper.cpp on the server.