Native payment code_url uses weixin:// protocol which is a WeChat deep link,
not openable in browsers. QR code is the standard approach - user scans
with WeChat and completes payment within the app.
- Change API endpoint from /v3/pay/transactions/h5 to /v3/pay/transactions/native
- Remove scene_info (not needed for native mode)
- Return code_url instead of h5_url
- recharge.dspy: display QR code image via api.qrserver.com
- user_recharge.dspy: return both code_url and qr_url
