* Improved navigation and search result highlighting in the EPUB reader
* refactor: implement JIT chunk restoration for robust navigation
- Fixes search and bookmark navigation failing in same-chapter transitions.
- Introduced JIT (Just-in-Time) HTML restoration in `epub_reader.js` to
re-populate virtualized chunks before CFI resolution or search scrolling.
- Synchronized search highlighting and user highlights within
newly-restored chunk segments.
- Improved search navigation accuracy by mapping occurrences to
relative chunk indices.
* Implemented a custom text selection engine for the paginated EPUB reader to support cross-page selection and improved handle interaction.
* Implemented management of external file behavior and improved library filtering.
* Added support for toolbar customization in the EPUB reader.
* Added support for toolbar customization in the PDF reader.
* fix: rendering during auto-scroll and navigation on long pages
* Added a "Scroll to Top" feature to the auto-scroll controls in both EPUB and PDF readers.
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