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/prefabs/items/WelcomeBoard.gd

@@ -0,0 +1,13 @@
+extends StaticBody2D
+
+func interact():
+	# Prevent multiple dialogs
+	if get_tree().root.has_node("WelcomeDialog"):
+		return null
+		
+	# Spawn the Welcome Dialog
+	var dialog = preload("res://scenes/ui/welcome_dialog.tscn").instantiate()
+	dialog.name = "WelcomeDialog"
+	# Add to the Scene Root (World) or CanvasLayer if it has one
+	get_tree().root.add_child(dialog)
+	return null # Return null prevents Player from showing a bubble