fix: enforce take_profit_pct in HOLD evaluation loop (#163)

HOLD 판정 후 보유 포지션에 대해 stop_loss와 함께 take_profit도 체크하도록 수정.
AI가 생성한 take_profit_pct가 실제 거래 로직에 반영되지 않던 구조적 결함 수정.

- HOLD 블록에서 loss_pct >= take_profit_threshold 조건 추가
- stop_loss와 상호 배타적으로 동작 (stop_loss 우선 체크)
- take_profit 기본값 3.0% (playbook 없는 경우 적용)
- 테스트 2개 추가:
  - test_hold_overridden_to_sell_when_take_profit_triggered
  - test_hold_not_overridden_when_between_stop_loss_and_take_profit

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main.py

@@ -387,8 +387,10 @@ async def trading_cycle(
             if entry_price > 0:
                 loss_pct = (current_price - entry_price) / entry_price * 100
                 stop_loss_threshold = -2.0
+                take_profit_threshold = 3.0
                 if stock_playbook and stock_playbook.scenarios:
                     stop_loss_threshold = stock_playbook.scenarios[0].stop_loss_pct
+                    take_profit_threshold = stock_playbook.scenarios[0].take_profit_pct
 
                 if loss_pct <= stop_loss_threshold:
                     decision = TradeDecision(
@@ -406,6 +408,22 @@ async def trading_cycle(
                         loss_pct,
                         stop_loss_threshold,
                     )
+                elif loss_pct >= take_profit_threshold:
+                    decision = TradeDecision(
+                        action="SELL",
+                        confidence=90,
+                        rationale=(
+                            f"Take-profit triggered ({loss_pct:.2f}% >= "
+                            f"{take_profit_threshold:.2f}%)"
+                        ),
+                    )
+                    logger.info(
+                        "Take-profit override for %s (%s): %.2f%% >= %.2f%%",
+                        stock_code,
+                        market.name,
+                        loss_pct,
+                        take_profit_threshold,
+                    )
     logger.info(
         "Decision for %s (%s): %s (confidence=%d)",
         stock_code,