支持客户按套餐类型缩小可购范围

Constraint: 查询参数可选且仅接受 formal 或 addon
Rejected: 新增专用 Store 方法 | 现有 PackageStore.List 已支持 package_type 过滤
Confidence: high
Scope-risk: narrow
Directive: 套餐类型取值继续与 pkg/constants 保持一致
Tested: go run cmd/gendocs/main.go，确认 OpenAPI 生成 package_type 查询参数
Not-tested: 按用户要求未执行自动化测试

docs/admin-openapi.yaml

@@ -29405,6 +29405,13 @@ paths:
                     maxLength: 50
                     minLength: 1
                     type: string
+                - description: 套餐类型 (formal:正式套餐, addon:附加套餐)
+                  in: query
+                  name: package_type
+                  schema:
+                    description: 套餐类型 (formal:正式套餐, addon:附加套餐)
+                    nullable: true
+                    type: string
             responses:
                 "200":
                     content: