refactor: one name per decision in the state and its log

- the Research Manager's plan and the Portfolio Manager's decision live only in investment_plan and final_trade_decision; the debate states no longer copy them as judge_decision
- the saved state log writes the Trader's plan as trader_investment_plan, its state key
- the report tree, the final display and the live CLI read the decisions from those fields

tests/test_structured_agents.py

@@ -292,7 +292,6 @@ def _make_rm_state():
             "bull_history": "Bull says...",
             "bear_history": "Bear says...",
             "current_response": "",
-            "judge_decision": "",
             "count": 1,
         },
     }