feat(frontend): add authentication context and API client

- Add AuthContext for managing user authentication state
- Add ProtectedRoute component for route protection
- Update API client with JWT token injection
- Add refresh token rotation support
- Add CSRF token handling

frontend/src/components/ProtectedRoute.tsx

@@ -0,0 +1,25 @@
+import React from 'react';
+import { Navigate } from 'react-router-dom';
+import { useAuth } from '../context/AuthContext';
+
+interface ProtectedRouteProps {
+  children: React.ReactNode;
+}
+
+export const ProtectedRoute: React.FC<ProtectedRouteProps> = ({ children }) => {
+  const { isAuthenticated, loading } = useAuth();
+
+  if (loading) {
+    return (
+      <div className="min-h-screen flex items-center justify-center">
+        <div className="text-gray-600 dark:text-gray-400">Loading...</div>
+      </div>
+    );
+  }
+
+  if (!isAuthenticated) {
+    return <Navigate to="/login" replace />;
+  }
+
+  return <>{children}</>;
+};