feat: 新增代理分配套餐上架状态（shelf_status）功能

- 新增数据库迁移：为 shop_package_allocation 表添加 shelf_status 字段
- 更新模型/DTO：ShopPackageAllocation 增加 ShelfStatus 字段及相关枚举
- 更新套餐分配 Service：支持上架/下架状态管理逻辑
- 更新套餐 Store/Service：根据 shelf_status 过滤可售套餐
- 更新购买验证 Service：引入上架状态校验逻辑
- 归档 OpenSpec 变更：2026-03-02-agent-allocation-shelf-status
- 同步更新主规范文档：allocation-shelf-status、package-management、purchase-validation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/store/postgres/package_store.go

@@ -58,11 +58,13 @@ func (s *PackageStore) List(ctx context.Context, opts *store.QueryOptions, filte
 
 	query := s.db.WithContext(ctx).Model(&model.Package{})
 
-	// 代理用户额外过滤：只能看到已分配的套餐
+	// 代理用户额外过滤：只能看到已分配（allocation.status=启用）的套餐
+	// 不按 tb_package.shelf_status 过滤，代理套餐可见性由 allocation.shelf_status 决定
 	userType := middleware.GetUserTypeFromContext(ctx)
 	shopID := middleware.GetShopIDFromContext(ctx)
-	if userType == constants.UserTypeAgent && shopID > 0 {
-		query = query.Joins("INNER JOIN tb_shop_package_allocation ON tb_shop_package_allocation.package_id = tb_package.id").
+	isAgent := userType == constants.UserTypeAgent && shopID > 0
+	if isAgent {
+		query = query.Joins("INNER JOIN tb_shop_package_allocation ON tb_shop_package_allocation.package_id = tb_package.id AND tb_shop_package_allocation.deleted_at IS NULL").
 			Where("tb_shop_package_allocation.shop_id = ? AND tb_shop_package_allocation.status = ?",
 				shopID, constants.StatusEnabled)
 	}
@@ -77,7 +79,12 @@ func (s *PackageStore) List(ctx context.Context, opts *store.QueryOptions, filte
 		query = query.Where("tb_package.status = ?", status)
 	}
 	if shelfStatus, ok := filters["shelf_status"]; ok {
-		query = query.Where("tb_package.shelf_status = ?", shelfStatus)
+		if isAgent {
+			// 代理用户按自己的 allocation.shelf_status 过滤，不使用平台全局值
+			query = query.Where("tb_shop_package_allocation.shelf_status = ?", shelfStatus)
+		} else {
+			query = query.Where("tb_package.shelf_status = ?", shelfStatus)
+		}
 	}
 	if packageType, ok := filters["package_type"].(string); ok && packageType != "" {
 		query = query.Where("tb_package.package_type = ?", packageType)