fix: 证书扫描含pub_key.pem；诊断明确缺少apiclient_cert.pem

服务器仅有私钥无商户证书时V3签名必失败，诊断输出操作指引。

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

jituan/services/wechat_pay.py

@@ -87,7 +87,9 @@ def resolve_merchant_cert_serial(private_key_path, configured_serial=''):
         for fname in sorted(os.listdir(cert_dir)):
             if not fname.lower().endswith('.pem'):
                 continue
-            if 'key' in fname.lower():
+            lower = fname.lower()
+            # 只跳过私钥文件；pub_key.pem 等仍尝试（有人误命名证书）
+            if lower in ('apiclient_key.pem',) or 'private' in lower:
                 continue
             candidates.append(os.path.join(cert_dir, fname))
     except OSError as exc: