The printed command only works from the directory holding the compose
file, which is the thing the user came to the page not knowing. Adds a
copy button, a saved Compose directory setting, BAMBUDDY_COMPOSE_DIR,
and best-effort detection from a bind mount's host path.
Compose records the directory on every container it creates, but reading
that label needs the Docker socket mounted in — root-equivalent access
for a convenience string. The mountinfo guess is a prefill only: its root
field is relative to the mounted device, so a compose dir on its own
mount loses that prefix, and nothing in the container can detect it.
The field is restricted to path characters. It is the one setting whose
purpose is to be pasted into a root shell, so "/opt/bambuddy; rm -rf /"
would otherwise render as a plausible update command.
