Release v4.68.2

Part of #95 (acceptance 2). Found by the vector rendering the templates on the live Stage (Cratis/Stage#504).

Fixed

• The darkened tag severity colours were written with light-dark(). The Stage's CSS pipeline lowers light-dark() for older browsers into a pair of custom properties that stays unset there, so a severity tag had no background (white text on the page, 1.09:1) in the Stage. The shell now sets the light values and overrides them under the Scene configuration's data-scene-color-scheme='dark' (Lara's own dark values), with no light-dark() in the stylesheet (a specification keeps it that way).
• The real-browser template audit did not draw the dark page: its host kept the colour scheme of its first render, so the "dark theme" rows re-judged the light page. The host now remounts per scheme (and a specification alternates light and dark to prove it); the whole dark matrix - every template, state and width - passes.