- Delete `data.service.ts` and `offline-data.service.ts`, consolidating functionality into `LocalSystem`.
- Refactor book, character, and conversation operations to adopt unified, multilingual, and session-enabled IPC handlers in `LocalSystem`.
- Simplify redundant legacy methods, enhancing maintainability and consistency.
- Implement `Book` class to manage book-related operations, including CRUD functionality, cover image handling, and metadata management.
- Add interfaces for `BookProps`, `GuideLine`, `Act`, and other related structures.
- Integrate support for encryption and decryption of sensitive data.
- Include multilingual support (`fr` and `en`) for error messages and content handling.
- Establish connection with `book.repository` and other repositories for streamlined database operations.
