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/test/tests/test_npc_character.gd

@@ -125,6 +125,55 @@ func test_walk_to_idle_animation_transition() -> bool:
 	avatar.free()
 	return a and b and c
 
+func test_skinned_model_loads_and_keeps_the_head_contract() -> bool:
+	var avatar := _avatar(Rules.NpcType.TOURIST, 33)
+	var a := TestUtils.check(avatar.loaded_model and not avatar.fallback_avatar,
+		"committed npc_base.glb is used")
+	var b := TestUtils.check(avatar.get_node_or_null("Rig/Head") != null,
+		"Rig/Head survives the skinned path")
+	var c := TestUtils.check(avatar._skeleton != null and avatar._bone_indices.has("Head")
+		and avatar._bone_indices.has("HipL") and avatar._bone_indices.has("HandR"),
+		"armature bones are bound")
+	avatar.free()
+	return a and b and c
+
+func test_skinned_outfit_tints_the_material_slots() -> bool:
+	var avatar := _avatar(Rules.NpcType.TOURIST, 44)
+	var mi := avatar.find_child("npc_base", true, false) as MeshInstance3D
+	var outfit := NpcAvatar.outfit_for(Rules.NpcType.TOURIST, 44)
+	var found := 0
+	var tinted := 0
+	for index in mi.mesh.get_surface_count():
+		var material := mi.get_surface_override_material(index) as StandardMaterial3D
+		if material == null:
+			continue
+		found += 1
+		if material.albedo_color != Color.WHITE:
+			tinted += 1
+	var a := TestUtils.check(found == 5, "five material slots stay separate")
+	var b := TestUtils.check(tinted == found, "every slot carries the outfit tint")
+	var c := TestUtils.check(outfit["shirt"] != Color.WHITE, "seed gives a non-white outfit")
+	avatar.free()
+	return a and b and c
+
+func test_forced_fallback_still_builds_the_procedural_rig() -> bool:
+	var profile := NpcProfile.new()
+	profile.id = "fallback_test"
+	profile.npc_type = Rules.NpcType.TOURIST
+	profile.display_name = "Fallback"
+	var avatar := NpcAvatar.new()
+	avatar.use_skinned_model = false
+	avatar.setup(profile, "enter", 5, Vector3(0, 0.5, 6),
+		Vector3(0, 0.5, 1.5), Vector3(0, 0.5, 1.2), "fallback_test")
+	var a := TestUtils.check(not avatar.loaded_model and avatar.fallback_avatar,
+		"fallback is recorded when the model is disabled")
+	var b := TestUtils.check(avatar.get_node_or_null("Rig/Head") != null,
+		"fallback still exposes Rig/Head")
+	var c := TestUtils.check(avatar.find_child("HipL", true, false) != null,
+		"fallback limb pivots exist")
+	avatar.free()
+	return a and b and c
+
 func test_rig_is_articulated() -> bool:
 	var avatar := _avatar(Rules.NpcType.TOURIST, 77)
 	var a := TestUtils.check(avatar.find_child("HipL", true, false) != null