chore: initial commit for phase05

apps/web/src/hooks/use-theme.ts

@@ -0,0 +1,25 @@
+import { useCallback, useSyncExternalStore } from 'react';
+
+function getTheme(): 'dark' | 'light' {
+  return document.documentElement.classList.contains('dark') ? 'dark' : 'light';
+}
+
+const listeners = new Set<() => void>();
+
+function subscribe(listener: () => void) {
+  listeners.add(listener);
+  return () => listeners.delete(listener);
+}
+
+export function useTheme() {
+  const theme = useSyncExternalStore(subscribe, getTheme);
+
+  const toggleTheme = useCallback(() => {
+    const next = getTheme() === 'dark' ? 'light' : 'dark';
+    document.documentElement.classList.toggle('dark', next === 'dark');
+    localStorage.setItem('theme', next);
+    listeners.forEach((l) => l());
+  }, []);
+
+  return { theme, toggleTheme };
+}