Print files: wheels properly up 78e7159

A sharp-eyed inspection of the print files found stowaways: the Hornet and Falcon STLs were shipping with their landing gear still down. Fixed:

1. The bug. The exporter hides the gear, hook and afterburner groups before triangulating — but the triangle walk only checked each mesh’s own visibility flag, and children of a hidden group kept their own flags set. The renderers hid the subtree; the file didn’t.
2. The fix. The walk now checks visibility all the way up the ancestor chain. The F/A-18 STL dropped from 58 KB to 29 KB and the F-16 from 50 KB to 21 KB — half the file was wheels.
3. Every file regenerated. All 22 models re-exported, every zip repacked (PRINTING.txt unchanged — scales and sizes never moved), and the free fishing-boat sample refreshed too. Only the two fighters were affected, but the whole fleet got a fresh, verified build.
4. Verified on the plate. Side-view wireframes of the new files show the fuselage belly sitting flush at z=0 with nothing hanging below — ready to print wheels-up, as the box always promised.