Library — Optimizations and Fixes

Memory and Stability

Reduced RAM usage during library scanning: the device no longer collects thousands of excess file paths, preventing sudden reboots that occurred with very large libraries (1000+ books).
Improved stability during index rebuild: the full scan no longer exhausts the processor's available memory, allowing the rebuild to complete without reboots.
Prevented watchdog reboots: cover generation and library sorting now keep the system timer alive even with very large libraries, preventing freezes and unexpected restarts.

More robust cover generation: covers are now generated one at a time for the visible page, with an automatic retry system in case of momentary failure. If a cover cannot be created after a few attempts (corrupt or unsupported file), the book is still shown with a placeholder.
Fixed cover regeneration after deletion: deleting covers (single, page, or all) now correctly restarts thumbnail creation for the current page.
Streamlined generation flow: the progress bar now accurately reflects the cover generation status for the page, without needlessly restarting from scratch.

Escape from empty filters: if a filter (e.g. "Favorites" or "Recently Read") produces no results, you can now press Back to return home or long-press to open the sort/filter popups, instead of being stuck on the empty screen.
Render caching: the header information (active filter, sort order, select