Add the connected-shell head prototype (head_proto) with sculpted sockets/nose/lips/ears

TODO.md

@@ -80,10 +80,15 @@ the rest of §C remains the broad review checklist.
 
 ### 3. Head and face prototype
 
-- [ ] Build one `npc_casual` head/face prototype as a connected head shell plus intentional feature
+- [-] Build one `npc_casual` head/face prototype as a connected head shell plus intentional feature
       geometry — not a sphere with floating facial balls. Use loop-based eye sockets/lids, a
       readable nose bridge/tip/ala, a mouth with upper/lower lip volumes, ears with concha depth,
       and brow/cheek/jaw planes that survive the 256² AO bake.
+      In progress: `tools/npc_parts.py build --part head_proto` displaces the shell (seg 48/rings 26)
+      into sockets, a nose bridge/tip/ala, upper/lower lips and ears; the eyeballs stay separate.
+      Vision-judged (iteration 2): the nose + ear now protrude in profile, but the cranium still
+      reads as a "ball with a nose". Next: flatten the face plane, taper the jaw/chin, widen the
+      nose bridge, and shape the back of the skull before the 1.5 m/1.85 m comparison.
 - [ ] Compare two or three subdivision/loop variants at 1.85 m front/three-quarter/profile and a
       1.5 m portrait. Pick the variant that reads best before changing all 12 characters; keep the
       rejected variants local.