Implement full internationalization for the Next.js backoffice:
- i18n infrastructure: type-safe dictionaries (fr.ts/en.ts), cookie-based locale detection, React Context for client components, server-side translation helper
- Language selector in Settings page (General tab) with cookie + DB persistence
- All ~35 pages and components translated via t() / useTranslation()
- Default locale set to English, French available via settings
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
- API: add POST /series/mark-read to batch mark all books in a series
- API: add GET /series cross-library endpoint with search, library and status filters
- API: add library_id to SeriesItem response
- Backoffice: mark book as read/unread button on book detail page
- Backoffice: mark series as read/unread button on series cards
- Backoffice: new /series top-level page with search and filters
- Backoffice: new /libraries/[id]/series/[name] series detail page
- Backoffice: opacity on fully read books and series cards
- Backoffice: live search with debounce on books and series pages
- Backoffice: reading status filter on books and series pages
- Fix $2 -> $1 parameter binding in mark-series-read SQL
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
