feat: club 表独立 mch_key 字段，后台明确区分 APIv2 收款与 APIv3 提现

- 新增 club.mch_key 列并迁移 config_json 历史数据，api_v3_key 保持独立
- club-manage 读写 mch_key；支付读 club.mch_key 优先，兼容 config_json 回落
- 提现查单返回商户号改读俱乐部 V3 配置；不影响其他业务逻辑

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

jituan/management/commands/seed_club_xq.py

@@ -43,6 +43,7 @@ class Command(BaseCommand):
             'wx_secret': getattr(settings, 'WEIXIN_SECRET', ''),
             'mch_id': getattr(settings, 'WEIXIN_MCHID', '') or wx_v3.get('MCHID', ''),
             'pay_app_id': wx_v3.get('APPID', '') or getattr(settings, 'WEIXIN_APPID', ''),
+            'mch_key': getattr(settings, 'WEIXIN_SHANGHUMIYAO', ''),
             'api_v3_key': wx_v3.get('API_V3_KEY', ''),
             'cert_serial_no': wx_v3.get('CERT_SERIAL_NO', ''),
             'private_key_path': wx_v3.get('PRIVATE_KEY_PATH', ''),
@@ -75,7 +76,7 @@ class Command(BaseCommand):
                 if v and not getattr(club, k, None):
                     setattr(club, k, v)
             # V3 字段允许用 settings 补全（证书路径等）
-            for field in ('api_v3_key', 'cert_serial_no', 'private_key_path', 'platform_cert_dir', 'pay_app_id'):
+            for field in ('mch_key', 'api_v3_key', 'cert_serial_no', 'private_key_path', 'platform_cert_dir', 'pay_app_id'):
                 val = defaults.get(field)
                 if val and not getattr(club, field, None):
                     setattr(club, field, val)