feat: check the Mercado Pago account from the Kanban

"Verificar conta" on the Mercado Pago card of the Integrations tab runs the
read-only account check (whether the token is a test user's, the card
methods, how the test card is classified) without a container console.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/api/operator.py

@@ -303,6 +303,16 @@ def tiny_test(user=Depends(operator)):
     audit('tiny_tested', operator=user, ok=all(v == 'ok' for v in results.values()))
     return {'ok': all(v == 'ok' for v in results.values()), 'results': results}
 
+@router.post('/api/operator/mercadopago/check')
+def mercadopago_check(user=Depends(operator)):
+    """The Mercado Pago account behind the configured token; reads only."""
+    if payment.name != 'mercadopago':
+        raise HTTPException(409, 'Mercado Pago não está configurado')
+    from ..mercadopago_probe import check
+    audit('mercadopago_check', operator=user)
+    return check(payment.access_token)
+
+
 @router.get('/api/operator/tiny/callback')
 def tiny_callback(code: str = Query('', max_length=4096), state: str = Query('', max_length=128),
                   error: str = Query('', max_length=128)):