feat: 增加欢迎板

- 增加欢迎板场景
- 增加与玩家的交互，点击E弹出弹出框

scenes/ui/WelcomeDialog.gd

@@ -0,0 +1,20 @@
+extends CanvasLayer
+
+func _ready():
+	# Connect close button (X)
+	var header_close = find_child("CloseButton", true, false)
+	if header_close:
+		header_close.pressed.connect(_on_close_pressed)
+		
+	# Connect Start button
+	var start_btn = find_child("StartButton", true, false)
+	if start_btn:
+		start_btn.pressed.connect(_on_close_pressed)
+
+func _on_close_pressed():
+	queue_free()
+
+func _input(event):
+	# Allow ESC to close
+	if event.is_action_pressed("ui_cancel"):
+		queue_free()