Add public Android APK download

frontend/src/pages/auth/LoginPage.jsx

@@ -9,6 +9,8 @@ export default function LoginPage() {
   const navigate = useNavigate();
   const [form, setForm] = useState({ email: '', password: '' });
   const [loading, setLoading] = useState(false);
+  const apiBaseUrl = (import.meta.env.VITE_API_URL || 'http://localhost:4000').replace(/\/$/, '');
+  const androidApkUrl = `${apiBaseUrl}/downloads/android-apk`;
 
   const handleChange = (e) => setForm((f) => ({ ...f, [e.target.name]: e.target.value }));
 
@@ -54,6 +56,9 @@ export default function LoginPage() {
           <button type="submit" className="btn btn-primary btn-full" disabled={loading}>
             {loading ? 'Ingresando...' : 'Iniciar sesión'}
           </button>
+          <a className="btn btn-secondary btn-full auth-download-btn" href={androidApkUrl}>
+            Descargar app Android
+          </a>
         </form>
         <p className="auth-link">
           ¿No tienes cuenta? <Link to="/register">Registrarse</Link>