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.

electron/database/database.service.ts

@@ -27,10 +27,9 @@ export class DatabaseService {
         if (this.db) {
             this.close();
         }
-
-        // Get user data directory
-        const userDataPath = app.getPath('userData');
-        const dbPath = path.join(userDataPath, `eritors-local-${userId}.db`);
+        
+        const userDataPath:string = app.getPath('userData');
+        const dbPath:string = path.join(userDataPath, `eritors-local.db`);
 
         this.db = new sqlite3.Database(dbPath);
         this.userEncryptionKey = encryptionKey;