When STACKS_DIR is set, local managed stacks are stored in a flat
$STACKS_DIR/<stackName>/ layout instead of $DATA_DIR/stacks/<env>/<stack>/.
Existing stacks are not moved automatically and continue to resolve from
their existing locations. Invalid or unwritable STACKS_DIR values produce a
warning and fall back to $DATA_DIR/stacks instead of aborting startup. With
this layout, local stack names must be unique across environments.
Hawser agents report their remote stacks directory on hello. That path is
persisted on the environment as hawser_stacks_dir so compose APIs and the UI
can show host paths rather than Dockhand staging paths. Staging paths are
remapped to and from the remote stack dir for compose files, backups, and
environment settings. Backup restore may write under either the default
staging root or the configured STACKS_DIR.
Co-authored-by: xd003 <xd003@users.noreply.github.com>
