修复多商户轮换死锁，并加固回调解密与证书校验。

余额不足等明确错误在查单宽限 PENDING 时会卡死不换号；现确认无单后切换，停用商户仍可解回调、请求带 notify_url。

Co-authored-by: Cursor <cursoragent@cursor.com>

utils/wechat_v3.py

@@ -102,8 +102,8 @@ def verify_wechat_sign(headers, body, wx_cfg=None):
     if wx_cfg:
         cfgs = [wx_cfg]
     else:
-        from utils.wechat_mch_service import list_enabled_wx_cfgs
-        cfgs = list_enabled_wx_cfgs()
+        from utils.wechat_mch_service import list_wx_cfgs_for_callback
+        cfgs = list_wx_cfgs_for_callback()
 
     for cfg in cfgs:
         cert_path = _resolve_platform_pub_path(cfg, serial=serial)
@@ -139,10 +139,10 @@ def decrypt_callback_with_merchants(associated_data, nonce, ciphertext):
     仅对启用商户密钥做 AES 尝试（通常很少），成功后返回 (plaintext, wx_cfg)。
     业务侧再用 out_bill_no 反查记录上的 mch_id，对齐一致性。
     """
-    from utils.wechat_mch_service import list_enabled_wx_cfgs
+    from utils.wechat_mch_service import list_wx_cfgs_for_callback
 
     last_err = None
-    for cfg in list_enabled_wx_cfgs():
+    for cfg in list_wx_cfgs_for_callback():
         try:
             text = decrypt_callback_ciphertext(associated_data, nonce, ciphertext, wx_cfg=cfg)
             return text, cfg