chore: Pin langchain dependencies to exact versions

requirements.txt

@@ -6,10 +6,10 @@ accelerate>=0.33.0
 bitsandbytes>=0.43.0
 sentence-transformers>=5.0.0
 pypdf>=5.0.0
-langchain-core>=0.2.0
-langchain-text-splitters>=0.2.0
-langchain-community>=0.2.0
-langchain-huggingface>=0.0.3
+langchain-core==1.0.5
+langchain-text-splitters==1.0.0
+langchain-community==0.4.1
+langchain-huggingface==1.0.1
 faiss-cpu>=1.8.0
 pymongo>=4.0.0
 dnspython>=2.0.0