Power Display: Integrate with Keyboard Manager for monitor control shortcuts

### Description of the new feature / enhancement

The new Power Display module is a strong addition in my opinion, but its usefulness could be significantly extended by having it integrate with Keyboard Manager. Specifically, allowing users to bind monitor-related actions to custom keyboard shortcuts would enable faster control without needing to open the PowerToys UI **at all**.

For example, users could assign shortcuts to:
- Switch between monitor input sources (e.g. DisplayPort to HDMI and vice versa)
- Increase or decrease brightness
- Turn a display on/off or trigger sleep for specific monitors

This would effectively expose Power Display controls as callable actions within Keyboard Manager, similar to how shortcuts can currently launch apps or remap keys.

From an implementation standpoint, this could be handled by:
- Adding Power Display actions as selectable commands within Keyboard Manager
- Supporting both discrete values (e.g. set brightness to X) and relative adjustments (e.g. +10% brightness)
- Allowing targeting of specific monitors in multi-display setups

This integration would align well with PowerToys' goal of reducing friction for power users and enabling deeper system customisation.

### Scenario when this would be used?

- Quickly switching a monitor between work and personal devices without using physical buttons
- Instantly dimming or turning off a secondary monitor during focused work or presentations
- Managing multi-monitor setups more efficiently, especially when monitors are hard to access physically
- Reducing reliance on inconsistent or cumbersome on-screen display (OSD) controls built into monitors
- Switching input sources when the UI will be invisible when another source is active

### Supporting information

_No response_