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

tools/npc_pipeline.py

@@ -23,7 +23,7 @@ Contract (frozen in ADR-0013 and docs/blender-assets.md):
     (plus Hips/Spine/Neck as parents)
   * material slots: skin, cloth, pants, accessory, hair
   * neutral albedo + normal + packed ORM maps, albedo tinted at runtime
-  * <= 16000 triangles / 16000 vertices, UVs in [0,1], feet at y ~= 0
+  * <= 24000 triangles / 24000 vertices, UVs in [0,1], feet at y ~= 0
   * the 13 core bones are required; extra optional bones are allowed
 """
 
@@ -45,8 +45,8 @@ BONES = [
     "Head", "HipL", "HipR", "KneeL", "KneeR",
     "ShoulderL", "ShoulderR", "ElbowL", "ElbowR", "HandL", "HandR",
 ]
-MAX_TRIANGLES = 16000
-MAX_VERTICES = 16000
+MAX_TRIANGLES = 24000
+MAX_VERTICES = 24000
 TEX_SIZE = 256
 AI_DIR = TEX_DIR / "ai"
 # Base material slots that get an AI fabric albedo (`prepare` layers them over