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

docs/npc-visual-review.md

@@ -71,8 +71,8 @@ The criteria below are for the stylized target, not photorealism. A change must
 pass every applicable item before a library rebuild is accepted.
 
 1. **Asset contract:** `npc_base` mesh node, the required bones, five tint slots,
-   front +Z, feet within 3 cm of y=0, 1.6–2.1 m height, at most 16,000 triangles
-   and 16,000 glTF vertices per character. The required 13 core bones stay fixed;
+   front +Z, feet within 3 cm of y=0, 1.6–2.1 m height, at most 24,000 triangles
+   and 24,000 glTF vertices per character. The required 13 core bones stay fixed;
    optional extra bones are allowed. Gear remains at most 1,500 triangles.
 2. **Proportion and silhouette:** head, neck, shoulders, torso, hips, limbs and
    feet read as one body; front/three-quarter/profile silhouettes agree with the