FR: add theme variable for active tab icon/text color

[Mariusthvdb]

As of 2025.5 new theme variables have been introduced, and important steps forward were made in the Frontend.
However, some odd variable naming was also introduced, and this is a request to make life a bit simpler for the users that modify the native toolbar.

Please consider adding a variable for the active tab icon/text color, just like we have the app-header-selection-bar-color

if we could have app-header-selection-text-color or app-header-selection-icon-color we could use that in our themes, and not have to resort to card-mod for making the selected tab stand out. It would be named in accordance with app-header-text-color that is the regular (unselected/generic)

The variable we have to use now is sl-color-primary-600 in a card-mod like:

      sl-tab[aria-selected=true] {
        --sl-color-primary-600: var(--active-color);

which is accompanied by sl-color-neutral-600, also not very intuitively named.

we can do

    sl-color-primary-600: var(--active-color)
    sl-color-neutral-600: var(--app-header-text-color)

in our themes, but that breaks all other modifications in card-mod based on conditions, so would no be preferable

Hope you can consider, thanks1