feat(bar): keep autohide bar visible on empty workspaces

[mariopaath23]

Describe your changes

Added a new optional auto-hide behavior that keeps the bar visible on empty workspaces, so the bar remains shown while viewing the desktop and returns to normal auto-hide behavior when the active workspace contains application windows.

The option is disabled by default, so existing behavior is unchanged unless explicitly enabled.

Details:

• Adds a new bar.autoHide.showOnEmptyWorkspace configuration option.
• The bar determines whether its active workspace is empty using the existing
• Hyprland state already maintained by Quickshell.
• When the bar is forced visible, it publishes its reserved vertical offset per screen through a small shared BarState singleton.
• The overview consumes that offset directly, so it stays positioned below the visible bar without duplicating workspace detection or spawning additional hyprctl processes.
• This is handled per monitor, so multi-monitor setups can have different bar offsets depending on the active workspace on each screen.

Before:
https://github.com/user-attachments/assets/dac7a523-1573-484e-b5ad-2d25a037477c

After:
https://github.com/user-attachments/assets/aa0217e7-9e40-480c-890e-727f45f60fcf

A new toggle is also added to the Settings to control this behavior

Is it ready? Questions/feedback needed?

Ready for Review.
Feedback would be appreciated on whether the shared per-screen bar offset state is the preferred approach for keeping the overview aligned with the bar, or if there is an existing shared state mechanism that would be better suited for this.