支持自动提现多商户轮换：配置入库、打款单强制记 mch_id、收款失败自动换号。

- 新增 wechat_pay_mch_config 表，迁移时从 settings 种子默认商户
- TixianAutoRecord 增加 mch_id；查单/回调解密后按记录对齐
- 后台接口 wxmchlb/wxmchbj/wxmchscwj（权限 8080a）与证书上传

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

peizhi/management/commands/seed_wechat_mch_from_settings.py

@@ -0,0 +1,29 @@
+"""
+将 settings.WECHAT_PAY_V3_CONFIG 迁移进 wechat_pay_mch_config 表。
+用法：
+  python manage.py seed_wechat_mch_from_settings
+  python manage.py seed_wechat_mch_from_settings --force
+"""
+from django.core.management.base import BaseCommand
+
+from utils.wechat_mch_service import seed_from_settings
+
+
+class Command(BaseCommand):
+    help = 'Seed WechatPayMchConfig from settings.WECHAT_PAY_V3_CONFIG'
+
+    def add_arguments(self, parser):
+        parser.add_argument(
+            '--force',
+            action='store_true',
+            help='覆盖同商户号已有记录',
+        )
+
+    def handle(self, *args, **options):
+        cfg = seed_from_settings(force=bool(options.get('force')))
+        if not cfg:
+            self.stderr.write(self.style.ERROR('settings.WECHAT_PAY_V3_CONFIG 不完整，未写入'))
+            return
+        self.stdout.write(self.style.SUCCESS(
+            f"OK mch_id={cfg.get('MCHID')} source={cfg.get('_source')} path={cfg.get('PRIVATE_KEY_PATH')}"
+        ))