The palette already lived in CSS custom properties, so dark mode is a
token-override block in the new theme.css, applied via data-theme on
the document element. A moon/sun toggle sits top right in the navbar;
an explicit choice persists in localStorage, otherwise the app follows
the OS preference live. An inline head script applies the theme before
first paint so a dark reload never flashes light.
Token hygiene sweep alongside: literal colours that broke under a dark
palette (timeline chip text, color-mix against white, calendar stripes
and bands, warning banners, nav background) moved into ten new tokens
with light-mode values unchanged. The flip clock keeps its fixed dark
look by design; the map keeps standard light tiles in both themes.
