feat: Add ThemeContext for dark/light theme toggle

frontend/src/contexts/ThemeContext.tsx

@@ -0,0 +1,34 @@
+import React, { createContext, useContext, useState, ReactNode } from 'react';
+
+interface ThemeContextType {
+  theme: 'light' | 'dark';
+  toggleTheme: () => void;
+}
+
+const ThemeContext = createContext<ThemeContextType | undefined>(undefined);
+
+interface ThemeProviderProps {
+  children: ReactNode;
+}
+
+export const ThemeProvider: React.FC<ThemeProviderProps> = ({ children }) => {
+  const [theme, setTheme] = useState<'light' | 'dark'>('dark');
+
+  const toggleTheme = () => {
+    setTheme(prevTheme => prevTheme === 'light' ? 'dark' : 'light');
+  };
+
+  return (
+    <ThemeContext.Provider value={{ theme, toggleTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+};
+
+export const useTheme = (): ThemeContextType => {
+  const context = useContext(ThemeContext);
+  if (!context) {
+    throw new Error('useTheme must be used within a ThemeProvider');
+  }
+  return context;
+};