we're about to port the chrome-extension. everything else mostly works

frontend/src/context/ThemeContext.jsx

@@ -0,0 +1,70 @@
+import React, { createContext, useState, useContext, useEffect } 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 stored = localStorage.getItem('theme');
+    if (stored) return stored;
+    
+    return 'system'; // Default to system preference
+  });
+
+  useEffect(() => {
+    const root = window.document.documentElement;
+    
+    if (theme === 'system') {
+      // Follow system preference
+      const isDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
+      root.classList.remove('light', 'dark');
+      root.classList.add(isDark ? 'dark' : 'light');
+      localStorage.setItem('theme', 'system');
+    } else {
+      // Use explicit theme
+      root.classList.remove('light', 'dark');
+      root.classList.add(theme);
+      localStorage.setItem('theme', theme);
+    }
+  }, [theme]);
+
+  // Listen for system theme changes when in system mode
+  useEffect(() => {
+    if (theme !== 'system') return;
+
+    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
+    const handleChange = () => {
+      const root = window.document.documentElement;
+      root.classList.remove('light', 'dark');
+      root.classList.add(mediaQuery.matches ? 'dark' : 'light');
+    };
+
+    mediaQuery.addEventListener('change', handleChange);
+    return () => mediaQuery.removeEventListener('change', handleChange);
+  }, [theme]);
+
+  const toggleTheme = () => {
+    setTheme(prev => {
+      if (prev === 'light') return 'dark';
+      if (prev === 'dark') return 'system';
+      return 'light';
+    });
+  };
+
+  const value = {
+    theme,
+    toggleTheme,
+    isDark: theme === 'dark' || (theme === 'system' && window.matchMedia('(prefers-color-scheme: dark)').matches),
+  };
+
+  return <ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>;
+};
+