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

.agents/skills/gig-line-blender-asset-contract/references/asset-contract.md

@@ -59,7 +59,7 @@ skin, cloth, pants, accessory, hair
 
 | Asset | Limit |
 | --- | --- |
-| Character (library and base fallback) | 16,000 triangles / 16,000 glTF vertices |
+| Character (library and base fallback) | 24,000 triangles / 24,000 glTF vertices |
 | Gear piece | 1,500 triangles |
 | Prop | 4,000 triangles |
 | Library prop/venue total | must stay inside the venue tests and library budget |