first commit

frontend/src/contexts/ThemeContext.jsx

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+import React, { createContext, useContext, useEffect, useState } from 'react'
+
+const ThemeContext = createContext()
+
+export const useTheme = () => {
+  const context = useContext(ThemeContext)
+  if (!context) {
+    throw new Error('useTheme must be used within a ThemeProvider')
+  }
+  return context
+}
+
+export const ThemeProvider = ({ children }) => {
+  const [theme, setTheme] = useState(() => {
+    // Check localStorage first, then system preference
+    const savedTheme = localStorage.getItem('theme')
+    if (savedTheme) {
+      return savedTheme
+    }
+    // Check system preference
+    if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
+      return 'dark'
+    }
+    return 'light'
+  })
+
+  useEffect(() => {
+    // Apply theme to document
+    if (theme === 'dark') {
+      document.documentElement.classList.add('dark')
+    } else {
+      document.documentElement.classList.remove('dark')
+    }
+    
+    // Save to localStorage
+    localStorage.setItem('theme', theme)
+  }, [theme])
+
+  const toggleTheme = () => {
+    setTheme(prevTheme => prevTheme === 'light' ? 'dark' : 'light')
+  }
+
+  const value = {
+    theme,
+    toggleTheme,
+    isDark: theme === 'dark'
+  }
+
+  return (
+    <ThemeContext.Provider value={value}>
+      {children}
+    </ThemeContext.Provider>
+  )
+}