fix(account, frontend): 兼容处理创建时间字段

在 `account.py` 中更新了创建时间的获取逻辑，兼容 `created_at` 和 `create_at` 字段。前端组件 `StatsDashboard.jsx` 中相应调整了创建时间的展示逻辑，确保在 `created_at` 字段为空时能够正确显示。此更新提升了数据展示的准确性与用户体验。

backend/api/routes/account.py

@@ -766,7 +766,8 @@ async def fetch_realtime_positions(account_id: int):
                     if matched is None:
                         matched = db_trades[0]
                     entry_time = matched.get('entry_time')
-                    created_at = matched.get('created_at')  # 创建时间，无 entry_time 时用于展示开仓时间
+                    # 创建时间：兼容 DB 列名 created_at / create_at
+                    created_at = matched.get('created_at') if matched.get('created_at') is not None else matched.get('create_at')
                     stop_loss_price = matched.get('stop_loss_price')
                     take_profit_price = matched.get('take_profit_price')
                     take_profit_1 = matched.get('take_profit_1')

frontend/src/components/StatsDashboard.jsx

@@ -742,7 +742,7 @@ const StatsDashboard = () => {
                         开仓时间: {(trade.entry_time || trade.created_at) ? formatEntryTime(trade.entry_time || trade.created_at) : '—'}
                       </div>
                       <div className="entry-time">
-                        创建时间: {trade.created_at ? formatEntryTime(trade.created_at) : '—'}
+                        创建时间: {(trade.created_at != null && trade.created_at !== '') ? formatEntryTime(trade.created_at) : '—'}
                       </div>
                     </div>
                     <div className="trade-protection-col">