feat: report Mercado Pago's notifications in the account check

Without access to the Mercado Pago panel, "Verificar conta" now also says
how many payment notifications arrived and passed the signature in the last
24 hours, how many were refused by it, and the last one received: the PIX
payments created in test mode notify the webhook, so this shows whether
Mercado Pago reaches the server.

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

app/api/operator.py

@@ -310,7 +310,18 @@ def mercadopago_check(user=Depends(operator)):
         raise HTTPException(409, 'Mercado Pago não está configurado')
     from ..mercadopago_probe import check
     audit('mercadopago_check', operator=user)
-    return check(payment.access_token)
+    result = check(payment.access_token)
+    # Whether Mercado Pago's notifications reach this server and pass the
+    # signature: every accepted one is recorded, a refused one is audited.
+    with db.connect() as c:
+        received = c.execute('''SELECT count(*) AS n, max(received_at) AS last FROM dtf_local.payment_events
+            WHERE provider='mercadopago' AND received_at > now()-interval '24 hours' ''').fetchone()
+        last = c.execute('''SELECT received_at,status,outcome FROM dtf_local.payment_events
+            WHERE provider='mercadopago' ORDER BY received_at DESC LIMIT 1''').fetchone()
+        refused = c.execute('''SELECT count(*) AS n FROM dtf_local.security_events
+            WHERE event='payment_webhook_rejected' AND created_at > now()-interval '24 hours' ''').fetchone()
+    result['webhooks'] = {'accepted_24h': received['n'], 'refused_24h': refused['n'], 'last': last}
+    return result
 
 
 @router.get('/api/operator/tiny/callback')