Refine web mobile download prompt and document pagination

frontend/src/pages/auth/LoginPage.jsx

@@ -1,4 +1,4 @@
-import { useState } from 'react';
+import { useMemo, useState } from 'react';
 import { useNavigate, Link } from 'react-router-dom';
 import { useAuth } from '../../contexts/AuthContext';
 import { Download, PenTool } from 'lucide-react';
@@ -11,6 +11,10 @@ export default function LoginPage() {
   const [loading, setLoading] = useState(false);
   const apiBaseUrl = (import.meta.env.VITE_API_URL || 'http://localhost:4000').replace(/\/$/, '');
   const androidApkUrl = `${apiBaseUrl}/downloads/android-apk`;
+  const showAndroidDownload = useMemo(() => {
+    if (typeof navigator === 'undefined') return false;
+    return /Android/i.test(navigator.userAgent || '');
+  }, []);
 
   const handleChange = (e) => setForm((f) => ({ ...f, [e.target.name]: e.target.value }));
 
@@ -60,10 +64,12 @@ 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}>
-            <Download size={14} />
-            Descargar app Android
-          </a>
+          {showAndroidDownload && (
+            <a className="btn btn-secondary btn-full auth-download-btn" href={androidApkUrl}>
+              <Download size={14} />
+              Descargar app Android
+            </a>
+          )}
         </form>
         <p className="auth-link">
           ¿No tienes cuenta? <Link to="/register">Registrarse</Link>