fix: V3签名从私钥配对证书自动取序列号，xq忽略club错误私钥路径

SIGN_ERROR根因是私钥与序列号不是同一套证书；扫描匹配 apiclient_cert.pem。
新增 manage.py wx_v3_pay_diag 探针验签。

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

utils/wechat_v3.py

@@ -1,3 +1,4 @@
+import logging
 import re
 import time
 import hashlib
@@ -13,6 +14,8 @@ from Crypto.Cipher import AES
 
 from django.conf import settings
 
+logger = logging.getLogger(__name__)
+
 
 def _get_v3_config(club_id=None):
     from jituan.services.wechat_pay import get_wechat_v3_config
@@ -39,6 +42,10 @@ def build_authorization(method, url, body, club_id=None):
     private_key = load_private_key(club_id)
     mchid = cfg['MCHID']
     serial_no = (cfg.get('CERT_SERIAL_NO') or '').strip().upper()
+    logger.warning(
+        '[WX_V3_SIGN] club=%s mchid=%s serial=%s key_path=%s',
+        club_id, mchid, serial_no, cfg.get('PRIVATE_KEY_PATH'),
+    )
 
     parsed = urlparse(url)
     path = parsed.path