Windows service support incomplete

[dkontango]

Summary

The Windows platform implementation in platform_impl.go creates a scheduled task for the tunnel but doesn't use a proper Windows service (sc.exe / NSSM). This means the tunnel won't auto-restart on failure or show up in services.msc.

Current behavior

• Creates a scheduled task that runs at logon
• No restart-on-failure
• Not visible in Windows Services

Expected behavior

• Install as a Windows service via sc.exe create or NSSM
• Auto-restart on failure with backoff
• Visible and manageable via services.msc
• schmutz-join should detect if running as admin and use the appropriate method

Notes

Low priority — Linux and macOS (systemd / launchd) work correctly.