Raise the NPC character budget to 24k and refine the prototype neck

docs/asset-tooling.md

@@ -200,8 +200,8 @@ flatpak run org.blender.Blender --background \
   --python "$PWD/tools/blender_assets.py" -- adapt \
   --file "$PWD/tmp/npc-research/makehuman_base.glb" \
   --out "$PWD/tmp/npc-research/makehuman_adapted.glb" \
-  --target-tris 16000
-# prints: adapted makehuman_adapted.glb: 36972 -> 16000 tris (bones=N, meshes=1)
+  --target-tris 24000
+# prints: adapted makehuman_adapted.glb: 36972 -> 24000 tris (bones=N, meshes=1)
 ```
 
 Run `inspect` on the adapted GLB before and after, and keep the procedural