- Reorganize and reformat IPC handlers for improved readability and structure.
- Add missing type definitions for `StoryData`, `AddWorldElementData`, `SetAIGuideLineData`, and others.
- Simplify handler functions by enforcing consistent parameter usage and return types.
- Remove outdated comments, redundant logic, and placeholder TODOs.
- 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.
- Add `LocalSystem` with handlers for session retrieval (`userId`, `lang`) and error handling.
- Extend IPC handlers to support multilingual operations (`fr`, `en`) and session data injection
