Avatar customization: skin tone, head swap, and hair now actually apply

Three dead controls on the customization screen:

- Skin tone slider did nothing: neither the visualizer nor AvatarSystem
  ever read loadout.skin_tone. Added AvatarLoader.apply_skin_tone() -- it
  retints the base body's skin surfaces (matched by the placeholder skin
  albedo, i.e. head + arms) -- and both build paths call it. Slider now
  maps across a deep-to-pale skin range.

- "Cyber Head" did nothing: its catalog entry was type "body_part", which
  load_attachment() rejects, and the placeholder body is one mesh so there
  was nothing to hide either. Retyped it as an attachment -> it mounts on
  the Head bone as a cyber visor.

- Mohawk / ponytail sat inside the head: the Head and HeadTop bones were
  well below the visual head (bone at 1.58, head crown at ~2.03). Moved
  Head to the head's centre and HeadTop just above the crown (mesh is
  rigidly bound, so it doesn't move), and retuned the hair/visor/glasses
  meshes and offsets to match.

Verified: avatar smoke 14/14 (source + pack), fresh-clone, 2p multiplayer,
and drove the real customization screen in rendered screenshots (equip
head+mohawk+mid skin, then ponytail+glasses+pale skin).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015jtxAiu5dAW4WxCNdGkrkJ

scripts/avatar/avatar_loader.gd

@@ -23,6 +23,11 @@ const AvatarCatalog := preload("res://scripts/avatar/avatar_catalog.gd")
 ## Maximum number of attachments allowed in the accessory slot.
 const MAX_ACCESSORY_COUNT := 8
 
+## The skin albedo baked into the placeholder base body by
+## gen_placeholder_avatars.gd. apply_skin_tone() finds the mesh surfaces
+## painted this colour (head + arms) and retints them.
+const PLACEHOLDER_SKIN_ALBEDO := Color(0.96, 0.80, 0.19)
+
 ## Skeleton bone names that form the canonical rig (§3.1).
 const CANONICAL_BONES := [
 	"Root",
@@ -239,6 +244,33 @@ func set_base_mesh_visible(slot_id: String, visible: bool) -> void:
 		mesh.visible = visible
 
 
+## Retint the base body's skin surfaces (the ones the generator painted
+## PLACEHOLDER_SKIN_ALBEDO -- head + arms) to [param color]. A no-op if the
+## colour is unset (transparent). Real segmented bodies will do this per mesh.
+func apply_skin_tone(color: Color) -> void:
+	if color.a <= 0.0:
+		return
+	if avatar_node == null or not is_instance_valid(avatar_node):
+		return
+	var skel := avatar_node.get_node_or_null("Skeleton3D") as Skeleton3D
+	if skel == null:
+		return
+	for child in skel.get_children():
+		if not (child is MeshInstance3D):
+			continue
+		var mi := child as MeshInstance3D
+		if mi.mesh == null:
+			continue
+		for s in mi.mesh.get_surface_count():
+			var mat := mi.get_active_material(s)
+			if mat is BaseMaterial3D and \
+					(mat as BaseMaterial3D).albedo_color.is_equal_approx(PLACEHOLDER_SKIN_ALBEDO):
+				var tinted := StandardMaterial3D.new()
+				tinted.albedo_color = color
+				tinted.roughness = 0.9
+				mi.set_surface_override_material(s, tinted)
+
+
 ## Get the current loadout as a dictionary (for serialization).
 func get_current_loadout() -> Dictionary:
 	var loadout: Dictionary = {