Contrast-preference query

The CSS `prefers-contrast` media query lets a site detect a viewer's requested contrast level (e.g. `more`) and suppress low-contrast decorative layers, a distinct web standard from Windows forced-colors mode.

grounded in: commit 13e906b 'Suppress the matrix/sky canvases under prefers-contrast: more' (plus 12d91c3 accessibility-tuning line in the self-improve loop)