fix: timezone handling and prediction logic

- api/models.py: Fix timezone conversion in stats queries by calculating UTC ranges in Python instead of using SQL CONVERT_TZ. Ensure JSON serializable types.
- api/prediction_service.py:
    - Update ensure_predictions_for_month to check previous day (ET) to cover CST month start.
    - Update _generate_prediction_for_hour to skip saving unclosed candles (current hour).
- trader/auto_trade_polymarket.py: Update to use hourly_model_predictions (V2) table for storing live trading predictions.

api/prediction_service.py

@@ -226,6 +226,17 @@ class PredictionService:
             preds = self.inference_manager.predict_all(df_input)
             
             # 7. 判断实际涨跌
+            # Check if the candle is closed (current time > candle open time + 1 hour)
+            current_now_utc = datetime.now(ZoneInfo('UTC')).replace(tzinfo=None)
+            candle_close_time = target_time_utc + timedelta(hours=1)
+            
+            is_closed = current_now_utc >= candle_close_time
+            
+            if not is_closed:
+                # 仅保存已完成的K线预测，未完成的跳过 (等待完成后再生成)
+                # 实时交易逻辑在 auto_trade_polymarket.py 中单独处理
+                return
+
             actual_result = 1 if target_close > prev_close else 0
             
             # 8. 组装数据 (宽表格式)
@@ -266,7 +277,11 @@ class PredictionService:
     
     def ensure_predictions_for_month(self, month: str) -> None:
         """
-        确保指定月份有预测数据
+        确保指定月份有预测数据 (CST)
+        需要检查:
+        1. 该月的所有日期 (ET)
+        2. 上个月的最后一天 (ET) -> 因为 ET 上个月最后一天 11:00-23:00 对应 CST 该月第一天 00:00-12:00
+        
         Args:
             month: 月份 (YYYY-MM)
         """
@@ -281,8 +296,15 @@ class PredictionService:
             from calendar import monthrange
             _, last_day = monthrange(year, mon)
             
+            # 1. 确保上个月最后一天有数据 (为了 CST 的开头)
+            first_day_of_month = datetime(year, mon, 1).date()
+            prev_day = first_day_of_month - timedelta(days=1)
+            prev_day_str = prev_day.strftime('%Y-%m-%d')
+            self.ensure_predictions_for_date(prev_day_str)
+            
             today = datetime.now(self.et_tz).date()
             
+            # 2. 确保本月所有日期
             for day in range(1, last_day + 1):
                 date = f"{year}-{mon:02d}-{day:02d}"
                 date_obj = datetime.strptime(date, '%Y-%m-%d').date()