fix: prevent flash of light theme on marketplace load

Add inline script to root layout that reads the stored theme preference
from cookie/localStorage synchronously before React hydrates, eliminating
the light→dark flash for users who prefer dark mode.

Also guard the theme storage write with the hydrated flag so the initial
render does not overwrite a stored 'dark' preference with 'light'.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/marketplace/src/components/MarketplaceShell.tsx

@@ -328,9 +328,12 @@ export default function MarketplaceShell({
 
   useEffect(() => {
     document.documentElement.classList.toggle('dark', theme === 'dark')
+    document.documentElement.style.colorScheme = theme === 'dark' ? 'dark' : 'light'
     document.body.dataset.theme = theme
-    writeScopedPreference(SHARED_THEME_KEY, theme, ['marketplace-theme'])
-  }, [theme])
+    if (hydrated) {
+      writeScopedPreference(SHARED_THEME_KEY, theme, ['marketplace-theme'])
+    }
+  }, [theme, hydrated])
 
   const value = useMemo(
     () => ({ language, theme, dict: dictionaries[language], companyName, setLanguage: applyLanguage, setTheme: applyTheme }),