task-93(店铺中心): 实现店铺凭证字段分离

新增 shop-credential-model.ts：凭证明文仅经凭证端点解码且落 SensitiveString，
与列表行(仅掩码)字段分离；shop-manage-api.ts 增加 fetchShopCredential
(GET /api/admin/shop-manages/{id}/credential?shop_name=…)。

TDD: task-93.test.ts 8 用例先 RED 后 GREEN。

admin-frontend-vue/src/pages/shop/shop-manage-api.ts

@@ -1,11 +1,13 @@
-/** 店铺列表/分组/新增适配（任务 88/90/91）：GET|POST /api/admin/shop-manages + 归一与解析。 */
+/** 店铺列表/分组/新增/编辑/凭证适配（任务 88-93）：/api/admin/shop-manages 系端点 + 归一与解析。 */
 import { http } from '@/api/http'
 import { unwrap } from '@/api/envelope'
 import { parseShopManagePage, toShopSummary } from './shop-manage-model.ts'
 import { parseShopManageGroups } from './shop-group-model.ts'
+import { toShopCredential } from './shop-credential-model.ts'
 import {
   normalizeShopListParams,
   toShopManagePageQuery,
+  type ShopCredential,
   type ShopGroupOption,
   type ShopManageListParams,
   type ShopPageResult,
@@ -61,3 +63,13 @@ export async function submitUpdateShopManage(id: number, form: ShopManageFormVal
   }
   return item
 }
+
+/** 读取店铺明文凭据：GET /api/admin/shop-manages/{id}/credential?shop_name=…；明文仅在内存短时使用。 */
+export async function fetchShopCredential(id: number, shopName: string): Promise<ShopCredential> {
+  const { data } = await http.get<unknown>(`${SHOP_MANAGE_ENDPOINT}/${id}/credential`, { params: { shop_name: shopName } })
+  const credential = toShopCredential(unwrap<unknown>(data))
+  if (!credential) {
+    throw new Error('读取店铺凭证响应异常：未返回有效记录')
+  }
+  return credential
+}