Integrate the `chatgpt_rs` library into the application and complete its development. This involves the following tasks: - [x] [#12](https://github.com/user/repo/issues/12) Add chatgpt_rs library as a dependency - [x] [#13](https://github.com/user/repo/issues/13) Implement chatgpt_rs integration in the application - [ ] [#14](https://github.com/user/repo/issues/14) Add error handling and user input validation - [ ] [#15](https://github.com/user/repo/issues/15) Implement conversation persistence and management - [ ] [#16](https://github.com/user/repo/issues/16) Testing and documentation Complete each task and close the corresponding issue. Once all tasks are completed, close this issue.