Wires the dark-mode plumbing:
- New $lib/theme module: themePreference + resolvedTheme stores plus
initTheme() / setThemePreference(). Owns localStorage persistence,
<html data-theme=...> mirroring, and the matchMedia listener that
re-resolves "system" when the OS preference flips. Storage-agnostic
(no Supabase coupling) so the caller persists to public.users.theme
separately.
- Inline anti-FOUC script in app.html reads localStorage + matchMedia
synchronously and writes data-theme before the first paint — refresh
in dark mode no longer flashes white.
- Tailwind switched to darkMode: ['selector', '[data-theme="dark"]']
so all existing `dark:` utilities resolve from the same attribute.
- :root and :root[data-theme=light] share the light token set; dark
tokens move into :root[data-theme=dark]. Tokens stay as RGB triplets
(rgb(var(--token) / <alpha>)) per the repo gotcha — no hsl().
- ThemeToggle.svelte: three-way radiogroup (Light / Dark / System) with
paraglide messages in EN + ES.
Tests (TDD): 8 new unit specs in src/lib/theme.test.ts cover defaults,
localStorage round-trip, data-theme reflection, system resolution
against matchMedia, invalid-value fallback, and OS preference change
propagation.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
