test(acceptance): align retained state fixtures

scripts/admin-test-env-modules/phase3-container-customs-fixture.mjs

@@ -39,9 +39,11 @@ async function raw(context, method, path, body, token, headers = {}) {
 
 async function loginMerchant(context) {
   const account = context.context?.merchantQualificationFixture
-  if (!account?.username || !account?.password) throw new Error('缺少本轮客户登录凭据')
+  const username = account?.username || process.env.MERCHANT_TEST_USERNAME || ''
+  const password = account?.password || process.env.MERCHANT_TEST_PASSWORD || ''
+  if (!username || !password) throw new Error('缺少客户登录凭据')
   const response = await context.request('POST', '/api/auth/login', {
-    username: account.username, password: account.password,
+    username, password,
   }, '')
   const token = success(response) ? response.body?.data?.accessToken : null
   if (!token) throw new Error(`本轮客户登录失败: requestId=${response?.requestId || 'missing'}, traceId=${response?.traceId || 'missing'}`)