Enhance synchronization logic and offline handling

- Refactor components to support conditional offline and online CRUD operations.
- Introduce `addToQueue` mechanism for syncing offline changes to the server.
- Add `isChapterContentExist` method and related existence checks in repositories.
- Consolidate data structures and streamline book, chapter, character, and guideline synchronization workflows.
- Encrypt additional character fields and adjust repository inserts for offline data.

electron/database/repositories/chapter.repository.ts

@@ -441,4 +441,20 @@ export default class ChapterRepo{
             }
         }
     }
+
+    static isChapterContentExist(userId: string, content_id: string, lang: "fr" | "en"): boolean {
+        try {
+            const db: Database = System.getDb();
+            const result: QueryResult | null = db.get('SELECT 1 FROM `book_chapter_content` WHERE `content_id`=? AND `author_id`=?', [content_id, userId]) || null;
+            return result !== null;
+        } catch (e: unknown) {
+            if (e instanceof Error) {
+                console.error(`DB Error: ${e.message}`);
+                throw new Error(lang === 'fr' ? `Impossible de vérifier l'existence du contenu du chapitre.` : `Unable to check chapter content existence.`);
+            } else {
+                console.error("An unknown error occurred.");
+                throw new Error(lang === 'fr' ? "Une erreur inconnue s'est produite." : "An unknown error occurred.");
+            }
+        }
+    }
 }