Bugfix release for the three open dogfooding issues.
- scad_cross_section accepts module/function/let definitions (#10)
- blender_boolean flags degenerate 0-face results as ok:false (#11)
- blender_validate caps per-face lists; verbose=True for full dumps (#12)
- Overhang math corrected (cos threshold, surface angle reporting)
- Empty meshes flagged in HEALTH instead of passing as watertight