owning_home_root() treated any candidate root holding facts.json as the
owner and returned None when the active root was one of them. A checkout
owned by a custom root (`install.sh --hermes-home <custom>`) and launched
from the platform default root borrowed correctly once; that launch's own
sync then wrote <default>/installs/<key>/facts.json, and every later launch
took the default root for the owner: its own tool store, launcher
publication and update tail, the behaviour this layer exists to stop.
The root the checkout sits in now outranks the platform default, and only
that one owner is compared with the active root.
Co-authored-by: FroRaut <79215537+Froraut@users.noreply.github.com>