hermes pm install (and activate/activate.ps1 behind it) now updates a
single live progress line instead of printing one line per ~4 MiB tick.
Detected via isatty(); stderr is the fallback because activate.ps1 pipes
stdout through Out-Host while stderr stays on the console. Off a TTY the
output is unchanged (same throttle, one line per tick) so CI logs are
unaffected.
