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/contents.query.gen.go

@@ -48,19 +48,19 @@ type contentQuery struct {
 	contentQueryDo contentQueryDo
 
 	ALL                 field.Asterisk
-	ID                  field.Int64
-	TenantID            field.Int64
-	UserID              field.Int64
-	Title               field.String
-	Description         field.String
-	Status              field.Field
-	Visibility          field.Field
-	PreviewSeconds      field.Int32
-	PreviewDownloadable field.Bool
-	PublishedAt         field.Time
-	DeletedAt           field.Field
-	CreatedAt           field.Time
-	UpdatedAt           field.Time
+	ID                  field.Int64  // 主键ID：自增；用于内容引用
+	TenantID            field.Int64  // 租户ID：多租户隔离关键字段；所有查询/写入必须限定 tenant_id
+	UserID              field.Int64  // 用户ID：内容创建者/发布者；用于权限与审计（例如私有内容仅作者可见）
+	Title               field.String // 标题：用于列表展示与搜索；建议限制长度（由业务校验）
+	Description         field.String // 描述：用于详情页展示；可为空字符串
+	Status              field.Field  // 状态：draft/reviewing/published/unpublished/blocked；published 才对外展示
+	Visibility          field.Field  // 可见性：public/tenant_only/private；仅控制详情可见，正片资源仍需按价格/权益校验
+	PreviewSeconds      field.Int32  // 试看秒数：默认 60；只对 preview 资源生效；必须为正整数
+	PreviewDownloadable field.Bool   // 试看是否允许下载：默认 false；当前策略固定为不允许下载（仅 streaming）
+	PublishedAt         field.Time   // 发布时间：首次发布时写入；用于时间窗与排序
+	DeletedAt           field.Field  // 软删除时间：非空表示已删除；对外接口需过滤
+	CreatedAt           field.Time   // 创建时间：默认 now()；用于审计与排序
+	UpdatedAt           field.Time   // 更新时间：默认 now()；编辑内容时写入
 
 	fieldMap map[string]field.Expr
 }