Moves three per-zone visual / report exporters (--export-png,
--export-zone-deps-md, --export-zone-spawn-png) out of
main.cpp into a new cli_zone_export.{hpp,cpp} module.
- export-png renders heightmap + normal-map + zone-map PNG
triplet for terrain previews
- export-zone-deps-md emits a GitHub-renderable model
dependency table (PR-friendly counterpart to --list-zone-deps)
- export-zone-spawn-png plots top-down spawn distribution PNG
bound to the zone's tile range
main.cpp shrinks by 267 lines (944 to 677) and crosses
below 700 lines on the way down. The previous --info-tilemap
dump used a 64x64 grid; this set complements it with content-
relative views.
