fix: remove unused nltk import causing ModuleNotFoundError

app/utils/preprocessing.py

@@ -2,7 +2,6 @@ from typing import List
 from .constants import stopwords, short_words_mappings
 from langchain_core.documents import Document
 from app.utils.model_factory import get_local_model
-from nltk.stem import PorterStemmer
 import spacy
 from pathlib import Path
 import re