Fix dashboard data findings from browser verification

- Próximas cuotas: headline is the upcoming billing batch (sum of every
  active plan's next cuota, using the rounding-absorbing last cuota
  when it's the pending one) — the in-cycle formula was ~always zero
  since cuotas bill on the 19th, day one of the next cycle.
- useAgent must name the 'wealthysmart' agent (default crashed the page).
- /transactions/recent excludes future-dated Tasa Cero cuotas.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/api/v1/endpoints/transactions.py

@@ -253,9 +253,15 @@ def recent_transactions(
     session: Session = Depends(get_session),
     _user: str = Depends(get_current_user),
 ):
+    from app.timeutil import utcnow
+
     query = (
         select(Transaction)
-        .where(Transaction.source == TransactionSource.CREDIT_CARD)
+        .where(
+            Transaction.source == TransactionSource.CREDIT_CARD,
+            # Tasa Cero generates future-dated cuotas; "recent" means billed.
+            Transaction.date <= utcnow(),
+        )
         .order_by(col(Transaction.date).desc(), col(Transaction.id).desc())
         .limit(limit)
     )