Always on Bottom

### Description of the new feature / enhancement

Introduce a feature that functions as the inverse of “Always on Top.” This would allow a window to be pinned behind all other windows, ensuring it remains visible in the background but never obstructs other active applications.

### Scenario when this would be used?

This feature would be especially useful when working with large, full-screen, or multi-monitor windows—such as Excel spreadsheets that span across two monitors.
In my workflow, I often need to reference other applications while filling out a large spreadsheet. Currently, I have to pin multiple smaller windows “Always on Top” to keep them visible. This becomes cluttered and inefficient.
With an “Always on Bottom” option, I could instead pin just the spreadsheet to the background and freely interact with other windows on top—keeping everything visible without constantly rearranging or managing multiple pinned windows.

### Supporting information

Multiple users have requested “Always on Bottom” functionality on online forums showing this is a common workflow idea. Adding this feature could directly address those limitations and improve window management efficiency.

The issue names no files, tests, or entry points. Start by locating the existing “Always on Top” implementation and its window-management behavior. Confirm the scope with maintainers, then verify that a window can remain behind other windows without obstructing active applications, including large or multi-monitor windows.

Written by the indexing model from the issue text.