feat: add dark mode support with theme toggle

src/contexts/theme-context.tsx

@@ -0,0 +1,74 @@
+'use client';
+
+import { createContext, useContext, useEffect, useState, type ReactNode } from 'react';
+
+type Theme = 'light' | 'dark' | 'system';
+
+interface ThemeContextType {
+  theme: Theme;
+  setTheme: (theme: Theme) => void;
+  resolvedTheme: 'light' | 'dark';
+}
+
+const ThemeContext = createContext<ThemeContextType | undefined>(undefined);
+
+const THEME_STORAGE_KEY = 'ruixin-theme';
+
+export function ThemeProvider({ children }: { children: ReactNode }) {
+  const [theme, setThemeState] = useState<Theme>('system');
+  const [resolvedTheme, setResolvedTheme] = useState<'light' | 'dark'>('light');
+
+  useEffect(() => {
+    const stored = localStorage.getItem(THEME_STORAGE_KEY) as Theme | null;
+    if (stored && ['light', 'dark', 'system'].includes(stored)) {
+      setThemeState(stored);
+    }
+  }, []);
+
+  useEffect(() => {
+    const root = document.documentElement;
+    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
+
+    const updateTheme = () => {
+      let resolved: 'light' | 'dark';
+
+      if (theme === 'system') {
+        resolved = mediaQuery.matches ? 'dark' : 'light';
+      } else {
+        resolved = theme;
+      }
+
+      setResolvedTheme(resolved);
+
+      if (resolved === 'dark') {
+        root.classList.add('dark');
+      } else {
+        root.classList.remove('dark');
+      }
+    };
+
+    updateTheme();
+
+    mediaQuery.addEventListener('change', updateTheme);
+    return () => mediaQuery.removeEventListener('change', updateTheme);
+  }, [theme]);
+
+  const setTheme = (newTheme: Theme) => {
+    setThemeState(newTheme);
+    localStorage.setItem(THEME_STORAGE_KEY, newTheme);
+  };
+
+  return (
+    <ThemeContext.Provider value={{ theme, setTheme, resolvedTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+}
+
+export function useTheme() {
+  const context = useContext(ThemeContext);
+  if (context === undefined) {
+    throw new Error('useTheme must be used within a ThemeProvider');
+  }
+  return context;
+}