Demo Banner Implementation
演示横幅实施
Add a banner to indicate prototype status while maintaining good design principles.
添加一个横幅以标明原型状态，同时遵循良好的设计原则。
Prompt
Insert a banner at the top of every page that says 'This is a demo prototype – data will not be saved.' Style it clearly but unobtrusively (e.g., light yellow background, dark text, closeable).