feat: add TenantLedger model and query generation

- Introduced TenantLedger model with fields for managing tenant transactions, including ID, TenantID, UserID, OrderID, transaction Type, Amount, and balance details.
- Implemented CRUD operations for TenantLedger with methods for Create, Update, Delete, and Reload.
- Generated query methods for TenantLedger to facilitate database interactions, including filtering, pagination, and aggregation functions.
- Established relationships with Order model for foreign key references.

backend/database/models/content_assets.query.gen.go

@@ -44,15 +44,15 @@ type contentAssetQuery struct {
 	contentAssetQueryDo contentAssetQueryDo
 
 	ALL       field.Asterisk
-	ID        field.Int64
-	TenantID  field.Int64
-	UserID    field.Int64
-	ContentID field.Int64
-	AssetID   field.Int64
-	Role      field.Field
-	Sort      field.Int32
-	CreatedAt field.Time
-	UpdatedAt field.Time
+	ID        field.Int64 // 主键ID：自增
+	TenantID  field.Int64 // 租户ID：多租户隔离；必须与 content_id、asset_id 所属租户一致
+	UserID    field.Int64 // 用户ID：操作人/绑定人；用于审计（通常为租户管理员或作者）
+	ContentID field.Int64 // 内容ID：关联 contents.id；用于查询内容下资源列表
+	AssetID   field.Int64 // 资源ID：关联 media_assets.id；用于查询资源归属内容
+	Role      field.Field // 资源角色：main/cover/preview；preview 必须为独立资源以满足禁下载与防绕过
+	Sort      field.Int32 // 排序：同一 role 下的展示顺序，数值越小越靠前
+	CreatedAt field.Time  // 创建时间：默认 now()；用于审计
+	UpdatedAt field.Time  // 更新时间：默认 now()；更新 sort/role 时写入
 
 	fieldMap map[string]field.Expr
 }