Add BooksSyncContext, refine database schema, and enhance synchronization support

- Introduce `BooksSyncContext` for managing book synchronization states (server-only, local-only, to-sync, etc.).
- Remove `UserContext` and related dependencies.
- Refine localization strings (`en.json`) with sync-related updates (e.g., "toSyncFromServer", "toSyncToServer").
- Extend database schema with additional tables and fields for syncing books, chapters, and related entities.
- Add `last_update` fields and update corresponding repository methods to support synchronization logic.
- Enhance IPC handlers with stricter typing, data validation, and sync-aware operations.

components/editor/TextEditor.tsx

@@ -300,7 +300,7 @@ export default function TextEditor() {
                     content,
                     totalWordCount: editor.getText().length,
                     currentTime: mainTimer
-                }, session?.accessToken ?? '');
+                }, session?.accessToken, lang);
             }
             if (!response) {
                 errorMessage(t('editor.error.savedFailed'));