Load and animate the Blender-authored NPC base mesh

Wire the skinned model from ADR-0013 into NpcAvatar:

- _build_skinned_body() instantiates the imported npc_base.glb, binds the 14
  armature bones, and keeps the procedural _build_body() as the offline
  fallback (use_skinned_model can force it in tests)
- outfit_for()/layer_for() tint the five material slots through the new
  SurfaceMaterials.npc_slot(); accessories and hand items attach under Rig/Head
- the existing limb pivots (Hip/Knee/Shoulder/Elbow/Hand + Head marker) keep the
  old animation math; _sync_skeleton() copies their rotations to bones. Bone
  pose rotation is absolute local orientation, so it is composed with the rest
  basis (otherwise the whole body snaps into a broken pose)
- skinned rigs scale uniformly (non-uniform parent scale shears the skin) and
  keep Rig/Head for the focus cone, nametag, and reaction tag
- commit the editable npc_base.blend plus a .gdignore: Godot's editor otherwise
  tries to import the blend and hangs during --import
- npc_pipeline audit tests (contract, textures, clean GLB, committed source)

Verification: headless 212/212, Python tooling 60/60, NPC budget 16 avatars =
144 meshes at ~6.9 ms, movement/focus/props smokes pass, compare 11 good / 0 bad.
TODO Phases 0-3 checked; environment lift and release remain.

src/game/materials.gd

@@ -31,6 +31,15 @@ const PROFILES := {
 	"rubber": {"roughness": 0.95, "metallic": 0.0},
 }
 
+## NPC material slot: keep the baked albedo/normal maps from the imported model
+## and tint them with the seed-driven outfit colour.
+static func npc_slot(source: Material, tint: Color) -> StandardMaterial3D:
+	var material := source.duplicate() as StandardMaterial3D
+	if material == null:
+		material = StandardMaterial3D.new()
+	material.albedo_color = tint
+	return material
+
 static func profile(role: String) -> Dictionary:
 	return PROFILES.get(role, PROFILES["concrete"])