런타임 에러 수정: langchain-core 의존성 추가

- pyproject.toml에 langchain-core 명시적 추가
- ModuleNotFoundError: No module named 'langchain_core' 해결

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

pyproject.toml

@@ -6,6 +6,7 @@ readme = "README.md"
 requires-python = ">=3.10"
 dependencies = [
     "langgraph",
+    "langchain-core",
     "langchain-openai",
     "langgraph-supervisor",
     "langchain-teddynote",