Add the local npc_parts.py head/face/hand part pipeline with tests and docs

docs/3d-model-review.md

@@ -151,8 +151,10 @@ width scale.
 | `makehuman_retargeted.glb` | 7,062 / 6,444 | 14 | 5 tint | arm-down + contract rig, deltoid warp remains |
 | `makehuman_final.glb` | 6,651 / 6,407 | 14 | 8 (incl. `skin.001`, `eye_white`, `rubber`) | project head/hands/shoes swapped; duplicate `skin.001` |
 
-Each GLB carries a stray 42-vert/80-tri `Icosphere` origin helper that must be dropped before any
-promotion.
+The "Icosphere" the inspector lists alongside these GLBs is the glTF importer's
+bone-display helper (a `pose_bone.custom_shape`), not part of the asset; `inspect_glb` already
+excludes it from measurements. The real cleanup for `makehuman_final.glb` is the duplicate
+`skin.001` material and the manual deltoid retopology.
 
 ## Overhaul acceptance criteria (measurable)