- Convert: warn when title+author already exists in library (preload check)
- Library: Duplicates sidebar section with grouped view and live counter
- Fix: Duplicates view cover loading now uses same canvas/two-pass pattern as renderBooksGrid
- Docs: add TODO-PERF-library-load.md with four identified bottlenecks
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
