Add all required dependencies for backend

requirements.txt

@@ -3,7 +3,7 @@ fastapi==0.110.0
 uvicorn==0.29.0
 python-dotenv==1.0.1
 
-# --- LangChain stack (old structure compatible with your retriever) ---
+# --- LangChain stack ---
 langchain==0.1.16
 langchain-community==0.0.32
 langchain-groq==0.1.0
@@ -12,9 +12,12 @@ faiss-cpu==1.7.4
 tiktoken==0.7.0
 rank-bm25==0.2.2
 
+# --- Fix for sentence-transformers dependency ---
+huggingface-hub==0.24.6
+
 # --- PDF + text processing ---
 pypdf==3.17.1
 unstructured==0.10.30
 
-# --- Optional frontend for testing ---
+# --- Optional frontend for local tests ---
 gradio==4.37.2