Support OLED brightness control via gamma

### Feature Description

I have an OLED laptop, so the traditional /sys/class/backlight/... does not work for changing brightness. Instead I use the hyprsunset utility, which is part of the Hyprland ecosystem. It would be nice for DMS to support automatic gamma changing in place of real brightness for OLED screens. Right now I just replaced these lines in `.config/hypr/dms/binds.conf`, but there is no DMS widget that pops up to indicate brightness/gamma.
```
# === Brightness Controls ===
bindel = , XF86MonBrightnessUp, exec, hyprctl hyprsunset gamma +10
bindel = , XF86MonBrightnessDown, exec, hyprctl hyprsunset gamma -10
```
Not a very important feature, but it would be a nice QOL improvement. Also not sure if this should be implemented compositor by compositor, or with agnostic package to control it.

Thanks for the great work put into DMS.

### Use Case

_No response_

### Compositor(s)

All compositors

### If Other, please specify

_No response_

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_

Start with the existing brightness bindings in .config/hypr/dms/binds.conf and the shown hyprctl hyprsunset gamma commands. Determine how gamma control could work across all compositors, then verify that OLED brightness changes trigger a DMS widget popup indicating the current gamma level.

Written by the indexing model from the issue text.