Moves the three asset-dependency analysis handlers
(--list-zone-deps, --list-project-orphans,
--remove-project-orphans) out of main.cpp into a new
cli_deps.{hpp,cpp} module. All three surface the relationship
between content references (objects.json + WOB doodad lists)
and on-disk model files: list-deps enumerates what a zone
needs, list-orphans flips that into 'what's on disk but
unreferenced', and remove-orphans deletes the resulting set
(with --dry-run for safe previews).
main.cpp shrinks by 355 lines (3,319 to 2,964) and finally
drops below 3K. The shared 'normalize basename' rule for
matching path references stays duplicated between the list
and remove handlers — a deliberate tradeoff, with comments
flagging the sync requirement.
