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.

lib/db/sync.service.ts

@@ -21,11 +21,8 @@ export async function getSyncStatus(): Promise<SyncProgress> {
     }
 
     try {
-        const result = await window.electron.dbGetSyncStatus();
-        if (!result.success) {
-            throw new Error(result.error);
-        }
-        return result.data;
+        const result = await window.electron.invoke<SyncProgress>('db:sync:status');
+        return result;
     } catch (error) {
         console.error('Failed to get sync status:', error);
         return {
@@ -46,11 +43,8 @@ export async function getPendingChanges(limit: number = 100) {
     }
 
     try {
-        const result = await window.electron.dbGetPendingChanges(limit);
-        if (!result.success) {
-            throw new Error(result.error);
-        }
-        return result.data || [];
+        const result = await window.electron.invoke<any[]>('db:sync:pending-changes', limit);
+        return result || [];
     } catch (error) {
         console.error('Failed to get pending changes:', error);
         return [];