fix(client): resolve TabContainer via find_child instead of @onready

@onready path resolution fails when the scene is instantiated as a
child of MainMenu — the node path is valid in the .tscn but the
layout hierarchy breaks during child instantiation in Godot 4.6.
Using find_child() is more robust for scenes that are dynamically
added to another scene's tree.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/ui/character_creation.gd

@@ -112,7 +112,7 @@ const RECENT_SLOTS := 9
 @onready var _rotate_left_btn: Button = $Layout/PreviewPanel/PreviewOverlay/RotateButtons/RotateLeftBtn
 @onready var _rotate_right_btn: Button = $Layout/PreviewPanel/PreviewOverlay/RotateButtons/RotateRightBtn
 @onready var _cam_angle_btn: Button = $Layout/PreviewPanel/PreviewOverlay/CamAngleBtn
-@onready var _tab_container: TabContainer = $Layout/TabPanel/TabContainer
+var _tab_container: TabContainer = null  # resolved in _ready() — @onready path fails when instantiated as child
 @onready var _footer_back: Button = $Footer/BackBtn
 @onready var _footer_randomize: Button = $Footer/RandomizeBtn
 @onready var _footer_start: Button = $Footer/StartBtn
@@ -195,6 +195,12 @@ var _tab_grids: Array[GridContainer] = [null, null, null, null, null]
 # =============================================================================
 
 func _ready() -> void:
+	# Resolve TabContainer — @onready path fails when scene is instantiated as child of MainMenu
+	_tab_container = find_child("TabContainer", true, false) as TabContainer
+	if _tab_container == null:
+		push_error("CharacterCreation: TabContainer not found in scene tree")
+		return
+
 	_descriptor = CharacterVisualDescriptor.new()
 	_descriptor.body_type = CharacterVisualDescriptor.BodyType.AVERAGE_M
 	_descriptor.skin_tone = 2  # light_olive — readable middle-ground default