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

docs/npc-model-sourcing.md

@@ -8,7 +8,7 @@ remain references or local prototypes unless a later ADR accepts them.
 
 The library needs variety beyond the original eight silhouettes while preserving
 the `npc_base` contract: mesh node, 13 required core bones (optional extras
-allowed), five tint slots, −Y/+Z front, grounded feet and the 16,000/16,000
+allowed), five tint slots, −Y/+Z front, grounded feet and the 24,000/24,000
 character budget.
 
 | Source | Licence | Result |
@@ -55,14 +55,16 @@ The MakeHuman body should reuse the approved local head/hand parts rather than f
 a second face implementation.
 
 The current local MPFB full-body prototype (`tmp/npc-research/build_mpfb_npc.py`) assembles the
-accepted head on an MPFB 2.0.18 body at **15,317 / 16,000 tris**, 1.810 m, 14 bones and 10
+accepted head on an MPFB 2.0.18 body at **19,747 / 24,000 tris**, 1.810 m, 14 bones and 10
 materials, with project hands, bevelled shoe shells with inset soles and tongues, pant cuffs,
 cloth sleeve cuffs and flat slot colours. The torso is radially inflated by 12% through z 0.72–1.40
-to loosen the shirt. It is a review candidate, not a shipped asset. The neck is a radial cut
-of the decimated column bridged by a four-ring, 20-segment lathe (lower rings painted cloth,
-reading as a crew neck); the ankles are hidden by 0.11 m shoe shells and 0.08 m pant cuffs, and a
-light smoothing pass softens the closed thigh/hip region. The neck skin test is guarded to z >
-1.35 so it cannot paint the crotch. Remaining polish: the crotch hollow still reads as a V under
+to loosen the shirt. It is a review candidate, not a shipped asset. The neck is a boolean-cut
+circular bore bridged by a smooth lathe; the accepted head is trimmed at the narrow neck (z 1.55)
+so its wide flat cut brim is discarded, and the lathe flares to cover the bore, then tucks inside
+the jaw. This removed the square collar, dark notches and wide brim; a thin jaw crease and a hard
+shirt-shoulder point in three-quarter view remain. The ankles are hidden by 0.11 m shoe shells and
+0.08 m pant cuffs, and a light smoothing pass softens the closed thigh/hip region. The neck skin
+test is guarded to z > 1.35 so it cannot paint the crotch. Remaining polish: the crotch hollow still reads as a V under
 the shirt hem, a partly loosened shirt and angular thigh facets; a separate loose shirt shell is
 the fix. Lowering the hem to z 0.80, tilting it up at the front and a 13% hem flare were rejected
 as a unitard, high-cut swimwear and a peplum respectively. A quick open, flared solidified tube