Ubuntu 26.04 sudo-rs leaves sudo su processes alive after SSH drop

Ubuntu 26.04 replaced traditional sudo with sudo-rs, which handles signals differently: when an SSH connection drops, sudo su processes do not exit and stay reparented to PID 1. Using sudo -i or sudo -s avoids the issue.

• sudo-rs in Ubuntu 26.04 fails to terminate sudo su on SSH disconnect
• Lingering sudo su processes get reparented to PID 1
• sudo -i leaves no lingering processes in the same test
• Switch implementations via sudo update-alternatives --config sudo