Fix on GIt Quickshell

[luyu-wu]

Recently this tool shows a grey screen on git Quickshell. Unsure of the quickshell commit that caused this, but after diagnosing the problem is like this:

• Screencopy is run asynchronously, only getting a frame ~80ms later
• PanelWindow is opaque by default (white)
• This causes a the user to not be able to see the screen when screenshotting.

This PR is a sketchy solution to these. The PanelWindow's color is set to "transparent", this is fine.
However, because the Screencopy lags, it captures the dimming and toolbars in the preview. To circumvent this, we delay the toolbars and dimming by using a isReady timer.

I think there may be a more elegant solution than this, but it works well enough for me! Feel free to make any changes.

[Ronin-CK]

we can bind isReady directly to the view's content state:

property bool isReady: screencopy.hasContent ScreencopyView { id: screencopy captureSource: root.targetScreen anchors.fill: parent z: -1 }
you can then remove the timer block entirely

[Ronin-CK]

Thanks @luyu-wu! Great catch on the grey screen issue.

I've accepted the fix but replaced the Timer with a more reactive ScreencopyView.hasContent binding to make it even smoother.