[Feature] Miracast screen casting

## Feature Description

It would be awesome if we could facilitate screencasting from a DMS widget.

## Use Case

Screencasting capabilities via miricast is available in many modern displays as a wireless connectivity option for mirroring or extending the current display configuration.

## Compositor

All compositors

## Proposed Solution

Add a "Cast" Control Center widget which, when activated, allows for scanning and connecting to available miricast targets, as well as display mode toggling (mirror vs extend).

## Alternatives/Existing Solutions

[gnome-network-displays](https://gitlab.gnome.org/GNOME/gnome-network-displays) seems to be the best solution available on Linux at the moment, and seems to support desktops other than Gnome.

Start by reviewing the DMS Control Center widget structure and existing display or compositor integration points; the issue names no files or tests. Compare the proposed Cast workflow with gnome-network-displays, with completion requiring target scanning, connection, and mirror-versus-extend mode switching across all compositors.

Written by the indexing model from the issue text.