Moves the two zone discovery / aggregation handlers
(--list-zones, --zone-stats) out of main.cpp into a new
cli_zone_list.{hpp,cpp} module. The first quickly enumerates
zones across the standard locations (custom_zones, output);
the second walks a project dir computing tile / creature /
quest / per-format byte totals with a per-zone breakdown
table — useful for content-pack release notes and capacity
planning.
main.cpp shrinks by 191 lines (3,624 to 3,433). Both --json
output modes preserved.
