renderer always causes floating group z-index bug

[chhsgithub]

same as this: https://dockview.dev/docs/advanced/iframe
which not noly iframe, but also normal dom element act not correctly
panel 1 is active, but covered by panel 2

[chhsgithub]

It seems that the z-index of element in floating panel is not following with panel container. Their z-index are always 999 and will not be changed by panel container(active or inactive)

And shift + moving floating body does not work with render: 'always'

[mathuo]

Fixed in 1.16.0