Refactor imports, streamline database IPC handlers, and improve offline support

- Replace absolute import paths with relative paths for consistency across files.
- Transition database operations in Electron main process to modular handlers in `ipc/book.ipc.ts` using the `createHandler` pattern.
- Update database sync service to use `window.electron.invoke()` for improved reliability and structure.
- Refactor `AddNewBookForm` to handle both online and offline book creation seamlessly.

electron/database/repositories/book.repository.ts

@@ -1,5 +1,5 @@
 import {Database, QueryResult, RunResult, SQLiteValue} from 'node-sqlite3-wasm';
-import System from "@/electron/database/System";
+import System from "../System.js";
 
 export interface BookQuery extends Record<string, SQLiteValue> {
     book_id: string;

electron/database/repositories/chapter.repository.ts

@@ -1,5 +1,5 @@
 import {Database, RunResult, SQLiteValue} from 'node-sqlite3-wasm';
-import System from "../System";
+import System from "../System.js";
 
 export interface ChapterContentQueryResult extends Record<string, SQLiteValue>{
     chapter_id: string;

electron/database/repositories/character.repository.ts

@@ -1,5 +1,5 @@
 import {Database, RunResult, SQLiteValue} from 'node-sqlite3-wasm';
-import System from "../System";
+import System from "../System.js";
 
 export interface CharacterResult extends Record<string, SQLiteValue> {
     character_id: string;

electron/database/repositories/location.repository.ts

@@ -1,5 +1,5 @@
 import {Database, RunResult, SQLiteValue} from 'node-sqlite3-wasm';
-import System from "../System";
+import System from "../System.js";
 
 export interface LocationQueryResult extends Record<string, SQLiteValue> {
     loc_id: string;

electron/database/repositories/user.repository.ts

@@ -1,5 +1,5 @@
 import {Database, RunResult, SQLiteValue} from 'node-sqlite3-wasm';
-import System from "../System";
+import System from "../System.js";
 
 export interface UserInfosQueryResponse extends Record<string, SQLiteValue> {
     first_name: string;