Add all required dependencies for backend

requirements.txt

@@ -1,13 +1,20 @@
-fastapi
-uvicorn
-python-dotenv
-langchain
-langchain-community
-langchain-groq
-sentence-transformers
-faiss-cpu
-tiktoken
-rank-bm25
-pypdf
-unstructured
-gradio
+# --- Core backend ---
+fastapi==0.110.0
+uvicorn==0.29.0
+python-dotenv==1.0.1
+
+# --- LangChain stack (old structure compatible with your retriever) ---
+langchain==0.1.16
+langchain-community==0.0.32
+langchain-groq==0.0.2
+sentence-transformers==2.2.2
+faiss-cpu==1.7.4
+tiktoken==0.7.0
+rank-bm25==0.2.2
+
+# --- PDF + text processing ---
+pypdf==3.17.1
+unstructured==0.10.30
+
+# --- Optional frontend for testing ---
+gradio==4.37.2