🐛 fix(model): preserve created_time on Model update and streamline field maintenance

The update operation for Model previously overwrote `created_time` with zero
because GORM included every struct field in the UPDATE statement.
This commit adjusts `Model.Update()` to:

* Call `Omit("created_time")` so the creation timestamp is never modified.
* Refresh `UpdatedTime` with `common.GetTimestamp()` before persisting.
* Delegate the remainder of the struct to GORM, eliminating the need to
  maintain an explicit allow-list whenever new fields are introduced.

No API contract is changed; existing CRUD endpoints continue to work
normally while data integrity for historical records is now guaranteed.

model/model_meta.go

@@ -50,8 +50,11 @@ func (mi *Model) Insert() error {
 
 // Update 更新现有模型记录
 func (mi *Model) Update() error {
+    // 仅更新需要变更的字段，避免覆盖 CreatedTime
     mi.UpdatedTime = common.GetTimestamp()
-    return DB.Save(mi).Error
+
+    // 排除 created_time，其余字段自动更新，避免新增字段时需要维护列表
+    return DB.Model(&Model{}).Where("id = ?", mi.Id).Omit("created_time").Updates(mi).Error
 }
 
 // Delete 软删除模型记录