fix(frontend): add error message display on login page

- Show error alert when login fails instead of console-only logging
- Display user-friendly error message: "Invalid email or password"
- Clear error state before new login attempt
- Use existing Alert component for consistency with RegisterPage

frontend/src/pages/LoginPage.jsx

@@ -4,22 +4,26 @@ import { useAuth } from '../contexts/AuthContext';
 import { Video, Mail, Lock } from 'lucide-react';
 import FormInput from '../components/common/FormInput';
 import LoadingButton from '../components/common/LoadingButton';
+import Alert from '../components/common/Alert';
 
 const LoginPage = () => {
   const [email, setEmail] = useState('');
   const [password, setPassword] = useState('');
   const [loading, setLoading] = useState(false);
+  const [error, setError] = useState('');
   const { login } = useAuth();
   const navigate = useNavigate();
 
   const handleSubmit = async (e) => {
     e.preventDefault();
+    setError('');
     setLoading(true);
     try {
       await login(email, password);
       navigate('/events');
     } catch (error) {
       console.error('Login failed:', error);
+      setError(error.message || 'Invalid email or password');
     } finally {
       setLoading(false);
     }
@@ -34,6 +38,8 @@ const LoginPage = () => {
           <p className="text-gray-600 mt-2">Sign in to your account</p>
         </div>
 
+        <Alert type="error" message={error} />
+
         <form onSubmit={handleSubmit} className="space-y-6">
           <FormInput
             label="Email"