When switching to power saver profile, the display brightness should automatically be reduced

### Problem

One of the most power hungry devices on a laptop is the display backlight.
Reducing its brightness can help a lot in extending the battery life.

### Proposal

When the user switches to the power saver profile, the display brightness should be reduced immediately - at least when the notebook is running on battery at that moment.

I am not sure by how many percent - it also depends on the surrounding light intensity (day vs. night) what would make sense I guess. At least you don't want to put the user into a situation where he cannot change back the brightness immediately because the screen is too dark while the sun is shining on the screen.

What might help there is that the scrollbar with the brightness could slowly start to fade to the left and stop fading once the user grabs the slider or manually changes the brightness using the function keys of the notebook keyboard

This also helps signaling the user that the power profile he has selected is now active.

### Prior Art (Optional)

_No response_