dsh-plugin-connection-banner: Displaying the DeepSeek Harness Reconnection Banner

This plugin is designed to address the lack of feedback in the DeepSeek Harness (DSH) Web UI when a connection is interrupted. It reuses the Harness public API to display a standard reconnection banner when the connection drops, which automatically disappears once the connection is restored. The plugin is lightweight and requires no polling; it takes effect immediately after installation and helps developers intuitively monitor the connection status.