Every app re-declared the same black/white/accent triple, so a palette now lives in
/lib/theme.lua and ui.lua derives muted, contrast, gradients and radius from it.
Deriving rather than listing means a new component costs no theme keys, and a theme
cannot pick text that is unreadable on its own accent.
Components take the palette by inheritance, so the three apps name no colors at all;
ui.theme stays for drawing outside the tree. Settings cycles the installed themes and
stores only the name.
evan