fix(kvm): close browser websocket immediately on AMT disconnect

[nmgaston]

NOTE: Use with sample-web-ui PR: device-management-toolkit/sample-web-ui#3159

Problem

When an AMT device disconnects (e.g. the device is powered off or the network drops), the KVM/SOL/IDER session would appear frozen in the browser UI. The browser websocket was only closed after ListenToBrowser unblocked from its ReadMessage call, which could take up to 30 seconds (the inactivity timeout) or indefinitely if the browser wasn't sending data.

Fix

In ListenToDevice, the deferred cleanup now immediately sends a websocket CloseMessage to the browser and closes the connection before cancelling the context. This means the browser receives the close frame as soon as the AMT device side drops, allowing the UI to update without waiting for ListenToBrowser to unblock.

Changes

• internal/usecase/devices/interceptor.go — updated the ListenToDevice defer to send websocket.CloseMessage and call Close() on the browser connection before cancel()
• internal/usecase/devices/interceptor_private_test.go — added TestListenToDeviceClosesWebSocketOnAMTDisconnect to verify WriteMessage(CloseMessage) and Close() are called on the browser websocket when the AMT side disconnects