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/Character.ts

@@ -2,9 +2,9 @@ import CharacterRepo, {
     AttributeResult,
     CharacterResult,
     CompleteCharacterResult
-} from "@/electron/database/repositories/character.repository";
-import System from "@/electron/database/System";
-import {getUserEncryptionKey} from "../keyManager";
+} from "../repositories/character.repository.js";
+import System from "../System.js";
+import {getUserEncryptionKey} from "../keyManager.js";
 
 export type CharacterCategory = 'Main' | 'Secondary' | 'Recurring';