Function detect_ssh_version 

pub fn detect_ssh_version() -> String

Detect SSH version by running ssh -V (output goes to stderr). Uses a 2-second timeout via mpsc channel to avoid hanging startup if the ssh binary is broken or on a slow filesystem.

On timeout, the spawned thread and child process continue running until ssh -V exits naturally. This is acceptable because ssh -V is near-instant and this only runs once at startup.