Introduce the shared design-token system under
ui/frontend/src/lib/theme/: tokens.css (dark default + light palette,
plus spacing/radii/typography scales), base.css global baseline
(document background, text, token focus ring, selection), and
theme.svelte.ts (system/light/dark choice, persisted to localStorage,
applied via data-theme on <html>). A pre-paint guard in app.html
resolves the theme before the app boots to avoid a flash, and the theme
picker is wired into the previously-disabled account-menu stub.
Migrate the always-visible in-game chrome to the tokens (header, account
menu, sidebar, tab-bar, bottom-tabs, shell background): dark renders as
before, light comes for free. The default stays dark during the
incremental migration; the remaining view bodies migrate in F1b.
Docs: ui/docs/design-system.md (+ index entry). Test: tests/theme.test.ts.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>