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/models/Location.ts

@@ -2,9 +2,9 @@ import LocationRepo, {
     LocationByTagResult,
     LocationElementQueryResult,
     LocationQueryResult
-} from "@/electron/database/repositories/location.repository";
-import System from "@/electron/database/System";
-import {getUserEncryptionKey} from "../keyManager";
+} from "../repositories/location.repository.js";
+import System from "../System.js";
+import {getUserEncryptionKey} from "../keyManager.js";
 
 export interface SubElement {
     id: string;