Fix: Update healthcheck message to DeepShelf API

src/book_recommender/api/main.py

@@ -157,7 +157,7 @@ async def health_check(request: Request):
 
         get_clusters_data()
 
-        return {"status": "OK", "message": "BookFinder API is healthy and core services are loaded."}
+        return {"status": "OK", "message": "DeepShelf API is healthy and core services are loaded."}
     except Exception as e:
         log_exception(e)
         raise HTTPException(