feat: 移除PDI和订单号字段，新增设备巡检模块

- 从物料跟踪页面移除订单号列和表单字段
- 从导航菜单移除PDI管理，添加设备巡检
- 新增InspectionLocation和InspectionRecord后端模型和API
- 新增设备巡检前端页面（左侧点位列表，右侧设备和历史记录）

backend/app/models/user.py

@@ -0,0 +1,15 @@
+from sqlalchemy import Column, Integer, String, Boolean, DateTime, func
+from app.database import Base
+
+
+class User(Base):
+    __tablename__ = "users"
+
+    id = Column(Integer, primary_key=True, index=True)
+    username = Column(String(50), unique=True, nullable=False, index=True)
+    full_name = Column(String(100))
+    hashed_password = Column(String(255), nullable=False)
+    role = Column(String(20), default="operator")  # admin/engineer/operator/viewer
+    is_active = Column(Boolean, default=True)
+    created_at = Column(DateTime, server_default=func.now())
+    updated_at = Column(DateTime, server_default=func.now(), onupdate=func.now())