Remove DataService and OfflineDataService, refactor book and character operations to use streamlined handlers in LocalSystem

- 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.

components/book/AddNewBookForm.tsx

@@ -27,7 +27,7 @@ import GuideTour, {GuideStep} from "@/components/GuideTour";
 import {UserProps} from "@/lib/models/User";
 import {useTranslations} from "next-intl";
 import {LangContext, LangContextProps} from "@/context/LangContext";
-import {getOfflineDataService} from "@/lib/services/offline-data.service";
+// TODO: Refactor to use window.electron.invoke() instead of OfflineDataService
 
 interface MinMax {
     min: number;