I need a production-ready VPN client built on the Sing-box core that works reliably inside mainland China. The app must run smoothly on Android, iOS and Windows even under strong filtering, DNS poisoning and carrier-level throttling. User experience should be instant, stable and interruption-free. Required VPN protocols: - Reality - Hysteria2 - VLESS - WireGuard Smart-connect requirements (lightweight only): - Auto-connect on launch - Monitor tunnel health and automatically switch to a healthy fallback node if the active one drops (No heavy latency-scanning or complex schedulers needed at this stage.) The app will simply fetch its JSON subscription from my existing XBoard-compatible API. User authentication is already in place, so the client only needs to read the subscription URL, parse nodes and apply the latest rules. No backend development required. Branding (logo, app name, colors) should be loaded from a simple config so future re-skinning is easy. Please keep the architecture clean, maintainable, and stable for China network conditions. This project does NOT require: - Node automation - Advanced smart routing - Full control-panel development I only need a reliable, clean, China-optimized three-platform VPN client using Sing-box. If you have previous experience with China-network VPN optimization, please highlight it.