➕ Add langchain-tavily for LLM service

- Add langchain-tavily==0.1.1
- Required by llm_service.py (line 7: from langchain_tavily import TavilySearch)
- Fixes ModuleNotFoundError at runtime

requirements.txt

@@ -18,6 +18,7 @@ langchain-community==0.3.13
 langchain-text-splitters==0.3.4
 langchain-huggingface==0.1.2
 langchain-groq==0.2.1
+langchain-tavily==0.1.1
 langgraph==0.2.50
 langsmith==0.2.11