Add a light set of the 6 per-scheme backdrops (public/backdrops/light/*.svg) —
soft, pastel-mid, non-figurative washes tuned to each accent so they read through
the light translucent glass. Wire them up centrally:
- App: the backdrop is on whenever bgImage && !perf (was dark-only), so light
gets it too.
- index.css: per-scheme rules are now [data-theme]-qualified — dark uses the dark
set, light the /light/ set; shared cover/fixed size rule for both.
- Settings: the Background image toggle + Image-fade slider work in light now
(removed the dark-only gates); hint no longer says 'dark only'. Trilingual.
The light glass (62% translucent tier) refracts the light backdrop just like dark
refracts its own; one fade slider controls both.
