Glass theme, after Apple's Liquid Glass (#43)

Translucent panels with backdrop-filter blur and saturation over a soft
coloured wash, light and dark, going solid under prefers-reduced-transparency
and prefers-contrast: more. The sticky filter bar and column headings are
frosted, since the list scrolls under them.

Text on a see-through panel lands on whatever the wash is behind it, so the
palette's hex values alone no longer say whether it clears AA. contrast.js
now samples the wash as the browser composites it on three viewport shapes.
It caught the first light palette at 3.7:1 for faint text, and a tinted
selection that failed everywhere; both were changed.

Left out: SVG displacement-map refraction, which Chromium alone applies to a
backdrop and only on fixed-size shapes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- A Glass theme, light and dark, with frosted see-through panels after Apple's Liquid Glass. It
+  goes solid when the system asks for less transparency or more contrast.
+
 ## [0.8.3] - 2026-09-19
 
 ### Security