fix: 看板动态时间改为北京时间 + 操作人显示中文姓名

1. 时区修复:
   - database.py: PG连接池会话级设置 TimeZone=Asia/Shanghai
   - dashboard_service.py: 格式化时间显式 astimezone(BEIJING_TZ)
   - 兜底: tzinfo为None时默认当作北京时间处理

2. 操作人中文姓名:
   - 收集所有operator_id → 调用mom_cache批量翻译
   - 优先中文姓名 → 英文用户名兜底
   - operator_id为None时不再显示"系统"，留空

backend/app/core/database.py

@@ -9,6 +9,9 @@ engine = create_async_engine(
     max_overflow=10,      # 超出 pool_size 时最多再创建的连接数
     pool_recycle=3600,    # 连接回收时间（秒），防止 MySQL 8 小时断连
     pool_pre_ping=True,   # 每次取出连接前先 ping 检测可用性
+    connect_args={
+        "server_settings": {"TimeZone": "Asia/Shanghai"},  # PG 会话级北京时间
+    },
 )
 
 AsyncSessionLocal = async_sessionmaker(

backend/app/services/dashboard_service.py

@@ -73,6 +73,7 @@ async def get_recent_activity(db: AsyncSession, limit: int = 10) -> list[RecentA
     from app.models.task_log import TaskLog
     from app.models.task import Task
     from app.models.product import Product
+    from app.core.time_utils import BEIJING_TZ
 
     stmt = (
         select(TaskLog, Task.task_name, Product.serial_number)
@@ -84,14 +85,33 @@ async def get_recent_activity(db: AsyncSession, limit: int = 10) -> list[RecentA
     result = await db.execute(stmt)
     rows = result.all()
 
+    # 收集 operator_id → 批量翻译中文姓名
+    operator_ids = list({row[0].operator_id for row in rows if row[0].operator_id})
+    name_map: dict[str, str] = {}
+    if operator_ids:
+        from app.services.mom_cache import get_display_names
+        name_map = get_display_names(operator_ids)
+
     activities: list[RecentActivity] = []
     for log, task_name, product_sn in rows:
         action_label = _action_label(log.action_type)
-        time_str = log.created_at.strftime("%m-%d %H:%M") if log.created_at else ""
+        # 强制转北京时间显示
+        t = log.created_at
+        if t:
+            if t.tzinfo is None:
+                t = t.replace(tzinfo=BEIJING_TZ)
+            else:
+                t = t.astimezone(BEIJING_TZ)
+            time_str = t.strftime("%m-%d %H:%M")
+        else:
+            time_str = ""
+        # operator_id: 优先显示中文姓名 → 英文用户名兜底 → 无记录时为空
+        op = log.operator_id
+        op_display = name_map.get(op, op or "")
         activities.append(RecentActivity(
             action=action_label,
             task_name=task_name or "",
-            operator=log.operator_id or "系统",
+            operator=op_display,
             product_sn=product_sn or "",
             time=time_str,
             remark=log.remark,