Moves the 3D-export bake handlers out of main.cpp:
--bake-zone-glb --bake-zone-stl --bake-zone-obj
--bake-project-obj --bake-project-stl --bake-project-glb
The STL + GLB project bakes share a combined dispatcher (one
function with internal STL-vs-GLB branching) since they walk
the same per-zone asset list and only differ in the output
emission code.
main.cpp drops 12,119 → 11,261 lines (-858). The combined-OR
opener spanning multiple lines created a parse-error fragment
in the extraction; caught + manually fixed before commit
(same pattern as the WOM info attachments/particles/sequences
extraction).
