Extend repository methods and synchronization logic with existence checks for books, chapters, characters, and related entities

- Add methods to verify the existence of acts, plot points, incidents, worlds, characters, locations, and their sub-elements in repositories.
- Update `syncBookFromServerToClient` to integrate existence checks with insert or update logic.
- Enhance multilingual error handling across repository methods.

electron/database/repositories/character.repository.ts

@@ -1,4 +1,4 @@
-import {Database, RunResult, SQLiteValue} from 'node-sqlite3-wasm';
+import {Database, QueryResult, RunResult, SQLiteValue} from 'node-sqlite3-wasm';
 import System from "../System.js";
 
 export interface CharacterResult extends Record<string, SQLiteValue> {
@@ -180,4 +180,35 @@ export default class CharacterRepo {
             }
         }
     }
+    static isCharacterExist(userId: string, characterId: string,lang: "fr" | "en"): boolean {
+        try {
+            const db: Database = System.getDb();
+            const result: QueryResult | null = db.get('SELECT 1 FROM `book_characters` WHERE `character_id`=? AND `user_id`=?', [characterId, 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 personnage.` : `Unable to check character existence.`);
+            } else {
+                console.error("An unknown error occurred.");
+                throw new Error(lang === 'fr' ? "Une erreur inconnue s'est produite." : "An unknown error occurred.");
+            }
+        }
+    }
+    
+    static isCharacterAttributeExist(userId: string, characterAttributeId: string,lang: "fr" | "en"): boolean {
+        try {
+            const db: Database = System.getDb();
+            const result: QueryResult | null = db.get('SELECT 1 FROM `book_characters_attributes` WHERE `attr_id`=? AND `user_id`=?', [characterAttributeId, 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 de l'attribut du personnage.` : `Unable to check character attribute existence.`);
+            } else {
+                console.error("An unknown error occurred.");
+                throw new Error(lang === 'fr' ? "Une erreur inconnue s'est produite." : "An unknown error occurred.");
+            }
+        }
+    }
 }