Allow Customization of Reading Interface (Themes, Fonts, Layouts)

[MiguelAntonioRS]

The PDF/ePub reader has limited customization options. Users should be able to personalize their reading experience.

Add the following options inside the reader: 
 

Light/Dark theme toggle
Font selection (Serif, Sans-serif, Monospace)
Font size adjustment
Line spacing control
Page layout options (single page, double page, scroll view)

These settings should persist across sessions.

[acx10]

All of these features are already available in the reader.