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-credential-model.ts

@@ -0,0 +1,42 @@
+/** 店铺明文凭据解析模型（任务 93）：凭证明文仅来自凭证端点且落 SensitiveString，
+ * 与列表行(仅掩码)字段分离；纯逻辑。 */
+import { unwrap } from '../../api/envelope.ts'
+import { toSensitiveString, type ShopCredential } from './shop-dto.ts'
+
+function text(value: unknown): string {
+  return typeof value === 'string' ? value.trim() : ''
+}
+
+function numberOrNull(value: unknown): number | null {
+  return typeof value === 'number' && Number.isFinite(value) ? Math.floor(value) : null
+}
+
+/** 解析单条明文凭据；缺 id 或密码为空视为无效(拒绝把空当明文)。 */
+export function toShopCredential(raw: unknown): ShopCredential | null {
+  if (!raw || typeof raw !== 'object') return null
+  const record = raw as Record<string, unknown>
+  const id = numberOrNull(record.id)
+  if (id === null) return null
+  const password = text(record.password)
+  if (!password) return null
+  const credential: ShopCredential = {
+    id,
+    groupId: numberOrNull(record.groupId ?? record.group_id),
+    groupName: text(record.groupName ?? record.group_name),
+    shopName: text(record.shopName ?? record.shop_name),
+    mallName: text(record.mallName ?? record.mall_name),
+    znUsername: text(record.znUsername ?? record.zn_username),
+    account: text(record.account),
+    password: toSensitiveString(password),
+  }
+  return credential
+}
+
+/** 解包凭证端点负载(data 为 ShopManageCredentialVo)为明文凭据；无效时抛可操作错误。 */
+export function parseShopCredential(payload: unknown): ShopCredential {
+  const credential = toShopCredential(unwrap<unknown>(payload))
+  if (!credential) {
+    throw new Error('读取店铺凭证响应异常：未返回有效的明文凭据')
+  }
+  return credential
+}