Fix Dark Mode colors hovering navigation bar status tabs
Summary:
* Use `{$orange}` variable for warning text instead of hardcoding text color.
* On hover, use `{$alphagrey}` variable for warning and fail text instead of hardcoding text color.
This makes text readable in both dark mode and default mode.
Refs T15056
Test Plan:
* Go to http://phorge.localhost/settings/panel/display/ and set `Accessibility` to `Dark Mode (Experimental)`
* Go to http://phorge.localhost/uiexample/view/PHUIListExample/, look at the "Status Tabs" section, hover over items
* Repeat previous step with `Default Mode` instead of Dark Mode
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15056
Differential Revision: https://we.phorge.it/D26372