Add Windows service to handle WireGuard tunnel operations with elevated privileges. Implement IPC server on TCP port 53189 for client-service communication using JSON protocol. Add install-service and uninstall-service commands to NSIS installer hooks for automatic service installation. Replace direct WireGuard calls with IPC requests when running on Windows. Add TunnelRequest and TunnelResponse types for IPC protocol
Add Ubuntu-to-Windows build workflow using cargo-xwin for i686-pc-windows-msvc target. Update build-tunnel-helper.sh with host OS detection, target validation, and cargo-xwin support for Linux cross-compilation. Add tauri.windows.conf.json to configure NSIS-only bundle output and npm script for Linux-based Windows builds. Update client-platforms.md to document cross-compilation support and clarify that MSI packaging still requires Windows environment.
