The operator user could serve a path or Unix socket if tailscaled
found a sudo rule for them, but the check used the GECOS display name
and so failed for most users with a 401. The check cannot be repaired
safely: listing another user's sudo rules never prompts, so it proves
a rule exists, not that the user has authenticated. An operator who
had not entered their sudo password could serve any root-readable file
or root-only socket. Require root instead and say so in the error.
Fixes#21204Fixes#21985Fixes#21988
Signed-off-by: Brendan Creane <bcreane@gmail.com>