fix: 修复聊天消息显示问题

- AuthScene: 修复节点路径错误 (WhaleFrame, UsernameInput)
- ChatManager: 修复 timestamp 类型转换 (String -> float)
- ChatMessage: 修复节点引用获取方式和 UI 显示
- ChatUI: 优化消息列表布局对齐

_Core/managers/ChatManager.gd

@@ -578,12 +578,12 @@ func _handle_chat_error(data: Dictionary) -> void:
 		"message": error_message
 	})
 
-# 处理接收到的聊天消息
+	# 处理接收到的聊天消息
 func _handle_chat_render(data: Dictionary) -> void:
 	var from_user: String = data.get("from", "")
 	var content: String = data.get("txt", "")
 	var show_bubble: bool = data.get("bubble", false)
-	var timestamp: float = data.get("timestamp", 0.0)
+	var timestamp: float = float(data.get("timestamp", "0.0"))
 
 	print("📨 收到聊天消息: ", from_user, " -> ", content)