fix(deps): update dependency langgraph to ^0.4.0

Author: renovate[bot]

pyproject.toml

@@ -39,7 +39,7 @@ langchain = "^0.3.13"
 langchain-community = "^0.3.16"
 langchain-core = "^0.3.31"
 langchain-openai = "^0.3.0"
-langgraph = "^0.3.0"
+langgraph = "^0.4.0"
 langgraph-checkpoint-postgres = "^2.0.13"
 litellm = "^1.53.5"
 markdown2 = "^2.5.2"