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/tests/backend/app/agents/test_state.py

@@ -0,0 +1,12 @@
+from langchain_core.messages import HumanMessage
+
+from app.agents.state import ConversationTurn, turn_to_message
+
+
+def test_turn_to_message_returns_human_message_for_user_turn():
+    turn = ConversationTurn(role='user', content='hello')
+
+    message = turn_to_message(turn)
+
+    assert isinstance(message, HumanMessage)
+    assert message.content == 'hello'