Refactor AuthContext into smaller files

Refactors the AuthContext.tsx file into smaller, more manageable files to improve code organization and maintainability. The functionality remains the same.

src/components/Header.tsx

@@ -1,7 +1,7 @@
 
 import React from 'react';
 import { Bell } from 'lucide-react';
-import { useAuth } from '@/contexts/AuthContext';
+import { useAuth } from '@/contexts/auth';
 
 const Header: React.FC = () => {
   const { user } = useAuth();