first commit

apps/docs/providers/theme-provider.tsx

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+'use client';
+
+import { createContext, useContext, useEffect, useMemo, useState } from 'react';
+
+type Theme = 'light' | 'dark' | 'system';
+
+interface ThemeContextValue {
+  theme: Theme;
+  resolvedTheme: 'light' | 'dark';
+  setTheme: (theme: Theme) => void;
+}
+
+const ThemeContext = createContext<ThemeContextValue | null>(null);
+
+export function ThemeProvider({ children }: { children: React.ReactNode }) {
+  const [theme, setThemeState] = useState<Theme>('system');
+  const [resolvedTheme, setResolvedTheme] = useState<'light' | 'dark'>('light');
+
+  useEffect(() => {
+    const stored = localStorage.getItem('docs-theme') as Theme | null;
+    if (stored) setThemeState(stored);
+  }, []);
+
+  useEffect(() => {
+    const root = document.documentElement;
+    const media = window.matchMedia('(prefers-color-scheme: dark)');
+    const apply = () => {
+      const next = theme === 'system' ? (media.matches ? 'dark' : 'light') : theme;
+      setResolvedTheme(next);
+      root.classList.toggle('dark', next === 'dark');
+    };
+    apply();
+    media.addEventListener('change', apply);
+    return () => media.removeEventListener('change', apply);
+  }, [theme]);
+
+  const setTheme = (next: Theme) => {
+    setThemeState(next);
+    localStorage.setItem('docs-theme', next);
+  };
+
+  const value = useMemo(() => ({ theme, resolvedTheme, setTheme }), [theme, resolvedTheme]);
+
+  return <ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>;
+}
+
+export function useTheme() {
+  const ctx = useContext(ThemeContext);
+  if (!ctx) throw new Error('useTheme must be used within ThemeProvider');
+  return ctx;
+}