WoweeCollision previously only contained terrain triangles; placed WMO
buildings had no collision in the exported zone, so players could walk
through walls. Added WoweeCollisionBuilder::addMesh() that transforms a
local-space mesh into world space with slope-based walkability flags,
and the editor's exportZone now walks every placed WMO and feeds each
group's geometry through it. Indoor vs outdoor groups are tagged via
the WMO group flag.