Update dependency langgraph to ^0.4.0

Author: renovate[bot]

pyproject.toml

@@ -36,7 +36,7 @@ ipython = "^9.0.0"
 langchain = "^0.3.13"
 langchain-openai = "^0.3.0"
 langchain-core = "^0.3.31"
-langgraph = "^0.3.0"
+langgraph = "^0.4.0"
 langgraph-checkpoint-postgres = "^2.0.13"
 litellm = "^1.53.5"
 markdown2 = "^2.5.2"