[Power Display] Show slider values persistently without requiring hover

### Description of the new feature / enhancement

Currently, the numerical value of a slider is only visible when hovering over the slider thumb.

Please display the current value persistently beside each slider, preferably at the right end of the slider as shown in the attached mockup. The value should update in real time while the slider is adjusted and use the same number format currently shown in the hover tooltip.

This could apply to brightness, contrast, volume, and any other numerical slider controls in Power Display.

### Scenario when this would be used?

When checking or matching settings across multiple monitors, users often need to see the exact values at a glance.

Requiring users to precisely hover over every slider thumb adds unnecessary effort, particularly when several monitors and controls are displayed. Persistent values would make the interface easier to scan and allow faster, more accurate comparisons and adjustments.

### Supporting information

_No response_

No source file, test, or entry point is identified in the issue; begin by locating the Power Display implementation and the existing slider hover tooltip behavior. Done means brightness, contrast, volume, and other numerical sliders show their current values persistently, update while adjusted, and use the existing tooltip number format.

Written by the indexing model from the issue text.