fix(windows): add loading spinner when killing process

[mazenS1]

Problem

When clicking the X button and confirming "Yes" to kill a process, there was no visual feedback that the operation was in progress.

Solution

Wire up the existing IsKilling property to the UI:

• Show animated spinner while process is being killed
• Hide kill button during the operation

Context

The IsKilling property existed in:

• Models/PortInfo.cs (lines 77-88) - the property definition
• ViewModels/MainViewModel.cs (line 191) - sets IsKilling = true before killing

Changes

• platforms/windows/PortKiller/MainWindow.xaml

Notes

• No new dependencies
• Uses existing InverseBoolToVisibilityConverter from the codebase

[dinesh-kondapalli]

Sure, i will look into this and fix it @productdevbook