support overlay layer for dank island pop ups

### Feature Description

add an option to allow notifications , OSDS , launcher , or any dankisland menu / popup to appear in fullscreen with wayland overlay layer.

### Use Case

because i dont want the island to appear all the time however i still want to see notifications or info from the dankisland whenever i need it on fullscreen.

### Compositor(s)

All compositors

### If Other, please specify

_No response_

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_

Start by tracing how notifications, OSDs, the launcher, and other DankIsland menus or popups are created and displayed, then review the Wayland overlay-layer behavior across the supported compositors. Done means there is a usable option that lets these surfaces appear on the overlay layer while the island itself remains hidden in fullscreen.

Written by the indexing model from the issue text.