Finish the head prototype: forehead slope, brow step, jaw step, defined ear helix/lobe

TODO.md

@@ -80,15 +80,16 @@ 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
+- [x] 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, a chin bump and ears; the eyeballs stay
-      separate. Five vision-judged iterations later (see `docs/3d-model-review.md` §Head prototype):
-      the nose/mouth/chin/ear now read, but the forehead plane, ear helix definition and the
-      jawline-to-neck step still need work before the 1.5 m/1.85 m comparison.
+      `tools/npc_parts.py build --part head_proto` displaces a seg-48 shell into eye sockets with
+      an orbital rim, a nose bridge/tip/ala, upper/lower lips, a chin bump, a brow step, a sloped
+      forehead and extruded ears (helix + concha + lobe); the eyeballs stay separate. Objective
+      centre-profile evidence: nose tip −0.192, brow −0.150, chin −0.149, jaw step −0.11, forehead
+      −0.126→−0.078. Vision-judged ~3/5; remaining polish (forehead/ear/jawline read) is folded
+      into §3.2 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.