* studio/frontend: keep theme classes mutually exclusive on <html>
The Sonner Toaster reads next-themes (mounted at provider.tsx with
attribute="class" defaultTheme="light"), so on first mount next-themes
adds a "light" class to <html>. Studio's own setTheme path
(features/settings/stores/theme-store.ts) only toggled "dark", so
after the user picked Dark in settings the document ended up with
html.className = "light dark". Harmless in CSS cascade because the
dark variables override, but reads as a UI defect in devtools and trips
CSS-aware tooling that branches on class lists.
Toggle "light" alongside "dark" in applyToDocument so the two classes
stay mutually exclusive regardless of how next-themes seeded the
initial class.
* studio/frontend: shorten theme-toggle comment
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Co-authored-by: danielhanchen <michaelhan2050@gmail.com>