Add reviewed MakeHuman head prototype (vision gate rejected)

docs/npc-model-sourcing.md

@@ -46,6 +46,10 @@ project head/hands swap reduced this to **6,407 / 16,000 tris and**
 **6,651 / 16,000 verts**, but manual shoulder/neck retopology and part cleanup
 remain before it can be considered shippable.
 
+A standalone MakeHuman head prototype is recorded in
+[`makehuman-head-review.md`](makehuman-head-review.md); it remains local/un-integrated
+until the overhaul accepts it.
+
 The head/face/hand overhaul in [`TODO.md`](../TODO.md) is the prerequisite: the
 MakeHuman body should reuse the approved local head/hand parts rather than
 forking a second face implementation.