Add book sorting and reader keyboard shortcuts with favorite indicator

[KrapfalAT]

Summary

• Sort bar added to the system detail view with four options: A–Z, Year, Pages, and Size — books within each category reorder instantly on click
• Keyboard shortcuts added to the reader: f to toggle favorite, t for table of contents, b for bookmarks, s for search — shortcuts are disabled when focus is inside an input field
• Favorite heart button added to the reader toolbar so users can favorite/unfavorite a book directly while reading without navigating back to the library

Notes

Keyboard shortcut state (sidepanel open/close) uses existing React state already present in the reader. The favorite button uses the existing FavoritesContext — no backend changes required.