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/BookList.tsx

@@ -13,7 +13,7 @@ import GuideTour, {GuideStep} from "@/components/GuideTour";
 import User from "@/lib/models/User";
 import {useTranslations} from "next-intl";
 import {LangContext, LangContextProps} from "@/context/LangContext";
-import {getOfflineDataService} from "@/lib/services/offline-data.service";
+import OfflineContext, {OfflineContextType} from "@/context/OfflineContext";
 
 export default function BookList() {
     const {session, setSession} = useContext(SessionContext);
@@ -22,6 +22,7 @@ export default function BookList() {
     const {setBook} = useContext(BookContext);
     const t = useTranslations();
     const {lang} = useContext<LangContextProps>(LangContext)
+    const {isCurrentlyOffline} = useContext<OfflineContextType>(OfflineContext)
     
     const [searchQuery, setSearchQuery] = useState<string>('');
     const [groupedBooks, setGroupedBooks] = useState<Record<string, BookProps[]>>({});
@@ -114,10 +115,12 @@ export default function BookList() {
     async function getBooks(): Promise<void> {
         setIsLoadingBooks(true);
         try {
-            const offlineDataService = getOfflineDataService();
-            const bookResponse: BookListProps[] = await offlineDataService.getBooks(
-                () => System.authGetQueryToServer<BookListProps[]>('books', accessToken, lang)
-            );
+            let bookResponse: BookListProps[] = [];
+            if (!isCurrentlyOffline()) {
+                bookResponse = await System.authGetQueryToServer<BookListProps[]>('books', accessToken, lang);
+            } else {
+                bookResponse = await window.electron.invoke<BookListProps[]>('db:book:books');
+            }
             if (bookResponse) {
                 const booksByType: Record<string, BookProps[]> = bookResponse.reduce((groups: Record<string, BookProps[]>, book: BookListProps): Record<string, BookProps[]> => {
                     const imageDataUrl: string = book.coverImage ? 'data:image/jpeg;base64,' + book.coverImage : '';