ThemeSwitcher: read the stored theme without setState in an effect #33

Problem

components/theme-switcher.tsx:13 sets the active theme in an effect:

useEffect(() => {
    setActive(getStoredTheme());
}, []);

That's an extra render on every page, and react-hooks/set-state-in-effect flags it.

Done when

• The stored theme is read without a synchronous setState in an effect (for example with useSyncExternalStore, which also keeps several tabs in sync).
• Switching themes still works and persists across reloads, with no flash or hydration warning.
• npx eslint components/theme-switcher.tsx is clean.
• If this is the last open set-state-in-effect issue, also set that rule back to "error" in eslint.config.mjs.

Size: ~15–25 lines.

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