feat: 优化库位树UI层级颜色，并将入库页面库位输入升级为级联选择器

inventory-backend/app/models/system.py

@@ -168,10 +168,14 @@ class SysWarehouseLocation(db.Model):
     level = db.Column(db.Integer, default=0)  # 层级深度，顶级为0
     is_enabled = db.Column(db.Boolean, default=True)
     created_at = db.Column(db.DateTime, default=datetime.now)
-    updated_at = db.Column(db.DateTime, default=datetime.now, onupdate=datetime.now)
+    # 注意：数据库表中没有 updated_at 字段，不要添加！
 
-    # 自关联
-    children = db.relationship('SysWarehouseLocation', backref=db.backref('parent', remote_side=[id]), lazy='dynamic')
+    # 自关联 - 使用 backref 定义父节点的反向引用
+    children = db.relationship(
+        'SysWarehouseLocation',
+        backref=db.backref('parent', remote_side=[id]),
+        lazy='dynamic'
+    )
 
     def to_dict(self):
         return {
@@ -181,6 +185,5 @@ class SysWarehouseLocation(db.Model):
             'full_path': self.full_path,
             'level': self.level,
             'is_enabled': self.is_enabled,
-            'created_at': self.created_at.isoformat() if self.created_at else None,
-            'updated_at': self.updated_at.isoformat() if self.updated_at else None
+            'created_at': self.created_at.isoformat() if self.created_at else None
         }