Remove DataService and OfflineDataService, refactor book and character operations to use streamlined handlers in LocalSystem

- Delete `data.service.ts` and `offline-data.service.ts`, consolidating functionality into `LocalSystem`.
- Refactor book, character, and conversation operations to adopt unified, multilingual, and session-enabled IPC handlers in `LocalSystem`.
- Simplify redundant legacy methods, enhancing maintainability and consistency.

tsconfig.json

@@ -47,6 +47,7 @@
     "public/**/*",
     "fonts/**/*",
     "electron/**/*",
+    "electron.d.ts",
     ".next/types/**/*.ts",
     ".next/dev/types/**/*.ts"
   ],