Feat/lesson 23

[jaydenellis]

I implemented the MediaItemsController to provide CRUD operations for the Library API, including GET /items, POST /items, GET /items/:id, and DELETE /items/:id endpoints. While building this, I fixed several critical issues in my initial implementation. I corrected the method invocation pattern so that the librarian performs actions on the library (librarian.addMediaItem and librarian.removeMediaItem) rather than passing the librarian as a parameter to library methods. I also fixed the MediaItem conversion in the POST endpoint to properly call request.getItem().asMediaItem(). Additionally, I added error handling in the DELETE endpoint to catch invalid UUID formats and return a 400 Bad Request response. All endpoints now return appropriate HTTP status codes and follow RESTful conventions as verified by the MediaItemsControllerTest suite.