update local startup flow and add root env example

Make the project start more reliably in the current Windows bash setup, add a safe root .env.example for onboarding, and lower the backend Python floor to 3.11 to match the validated local environment.

backend/app/agents/state.py

@@ -2,6 +2,8 @@ from dataclasses import dataclass
 from typing import TypedDict, Annotated
 from enum import Enum
 
+from langchain_core.messages import HumanMessage
+
 
 class AgentRole(str, Enum):
     MASTER = "master"