"System" option next to Dark and Light in theme toggle

[jonasreiher]

Feature Description

Add a third option "System" to the Dark and Light theme toggle on the bottom left.

Problem/Solution

By default, Hextra chooses its color theme based on the current system settings. By using the toggle, one can manually switch between the two modes.

However, having pressed the toggle once, you're stuck with one theme, there is no way to go back to the automatic change depending on system settings.

With this change, the toggle would have three states "System", "Dark", and "Light".

Alternatives Considered

Manually deleting the color-theme entry in local website storage.

Additional Context

My system changes between light and dark mode depending on time of day but sometimes I want to make an exception. If I use the toggle for this, I can't go back.

[imfing]

Thanks! this would be a nice enhancement