34e8a79994
Per review on #1715: the cap fed gamma-encoded luma into the WCAG contrast formula, so the >=3:1 target wasn't real (light-poimandres #340df2 was ~2.5:1 actual). Split the color helpers into colorLuma (perceptual, for light/dark classification — unchanged behavior) and relativeLuminance (WCAG-linearized sRGB, for contrast ratios). Session accents are now sized, and tests asserted, against relativeLuminance, so >=3:1 holds against the actual surface. Theme keeps luma for isLight/isLightTheme and exposes the WCAG status-line luminance for the cap.