Moves the four WOM interchange-format handlers (--export-obj,
--export-glb, --export-stl, --import-stl) out of main.cpp into
a new cli_wom_io.{hpp,cpp} module. WOM is our open M2
replacement; these are the bridge that lets it round-trip
through every external 3D tool — Blender, Three.js, slicers,
CAD packages — so the open format is actually useful.
main.cpp shrinks by 467 lines (9,464 to 8,997). The five WOB
and WHM exporters (--export-wob-glb, --export-whm-glb, etc.)
remain inline for a follow-up extraction.
