Implement Genre Management with CRUD Operations

- Add `Genre` entity with JPA annotations and database mapping.
- Create repository, service, and delegate handlers for Genre CRUD operations.
- Register handlers (`create_genre`, `get_genres`, `get_genre_by_id`, `update_genre`, `delete_genre`) in `DelegateActionManager`.
- Introduce Protobuf definitions for Genre messages.
- Update `DatabaseManager` to expose `EntityManager`.
- Enhance `DelegateActionManager` constructor to use `EntityManager` for handler initialization.

src/main/java/com/mediamanager/MediaManagerApplication.java

@@ -60,7 +60,7 @@ public class MediaManagerApplication {
                 default:
             }
             databaseManager.init();
-            actionManager = new DelegateActionManager();
+            actionManager = new DelegateActionManager(databaseManager.getEntityManager());
             actionManager.start();
             ipcManager = new IPCManager(config,actionManager);
             ipcManager.init();